eLife: latest articles by subject

Twelve phosphomimetic mutations induce the assembly of recombinant full-length human tau into paired helical filaments

mg@mrc-lmb.cam.ac.uk (Jane L Wagstaff) — Wed, 20 May 2026 00:00:00 +0000

The assembly of tau into amyloid filaments is associated with more than 20 neurodegenerative diseases, collectively termed tauopathies. Electron cryo-microscopy (cryo-EM) structures of brain-derived tau filaments revealed that specific structures define different diseases, triggering a quest for the development of experimental model systems that replicate the structures of disease. Here, we describe 12 phosphomimetic serine/threonine-to-aspartate mutations in tau, which we term PAD12, that collectively induce the in vitro assembly of full-length three-repeat tau into filaments with the same structure as paired helical filaments extracted from the brains of individuals with Alzheimer’s disease. Solution-state nuclear magnetic resonance spectroscopy suggests that phosphomimetic mutations in the carboxy-terminal domain of tau may facilitate filament formation by disrupting an intramolecular interaction between two IVYK motifs. PAD12 tau can be used for both nucleation-dependent and multiple rounds of seeded assembly in vitro, as well as for the seeding of tau biosensor cells. PAD12 tau can be assembled into paired helical filaments under various shaking conditions, with the resulting filaments being stable for extended periods of time. They can be labelled with fluorophores and biotin. Tau filaments extracted from the brains of individuals with Alzheimer’s disease have been known to be made of hyperphosphorylated and abnormally phosphorylated full-length tau, but it was not known if the presence of this post-translational modification is more than a mere correlation. Our findings suggest that hyperphosphorylation of tau may be sufficient for the formation of the Alzheimer tau fold. PAD12 tau will be a useful tool for the study of molecular mechanisms of neurodegeneration.

Natural xanthones as α-Mangostin induce vasorelaxation involving key gating residues in the S6 domain of BK channels

m.musinszki@physiologie.uni-kiel.de (Marianne A Musinszki) — Wed, 06 May 2026 00:00:00 +0000

Polyphenolic compounds are widely explored for health benefits, including hypertension, but their active ingredients, molecular targets, and mechanisms remain poorly defined. We identify the xanthone Mangostin from Garcinia mangostana as a potent modulator of several potassium channels, with large-conductance K⁺ (BK) channels as its primary target for vasorelaxation. Mangostin-activated BK channels as α subunits alone, in complexes with vascular β1 subunits, and in reconstituted BKα/β1–Ca_v nanodomains. It shifted BK voltage activation to more negative potentials by antagonizing channel closure and promoting channel opening without markedly altering Ca²⁺ sensitivity. Docking, competition, single-channel analysis, and mutagenesis localized the binding site in the pore cavity below the SF, involving gating-critical S6 residues I308, L312, and A316, and suggest that Mangostin stays bound in closed and open states. These findings establish BK channel activation as the core molecular mechanism driving Mangostin’s vascular effects and define its structural mode of action, informing nutraceutical safety assessment and BK-targeted drug design.

Towards a unified molecular mechanism for ligand-dependent activation of NR4A-RXR heterodimers

douglas.kojetin@vanderbilt.edu (Douglas J Kojetin) — Thu, 30 Apr 2026 00:00:00 +0000

A subset of nuclear receptors (NRs) function as permissive heterodimers with retinoid X receptor (RXR), defined by transcriptional activation in response to RXR agonist ligands. Permissive NR-RXR activation is generally understood to operate through a classical pharmacological mechanism in which RXR agonist binding enhances coactivator recruitment to the heterodimer. However, we previously demonstrated that transcriptional activation of permissive Nurr1-RXRα (NR4A2-NR2B1) heterodimers by an RXR ligand set, which included pharmacological RXR agonists and selective Nurr1-RXRα agonists that function as antagonists of RXRα homodimers, is explained by a non-classical activation mechanism involving ligand-binding domain (LBD) heterodimer dissociation (Yu et al., 2023). Here, we extend mechanistic ligand profiling of the same RXR ligand set to the evolutionarily related Nur77-RXRγ (NR4A1-NR2B3) heterodimer. Biochemical and NMR protein-protein interaction profiling, together with cellular transcription studies, indicate that activation of Nur77-RXRγ transcription by the RXR ligand set, which lacks selective Nur77-RXRγ agonists, is consistent with contributions from both classical pharmacological activation and LBD heterodimer dissociation. However, reanalysis of our previously published data for Nurr1-RXRα revealed that inclusion of selective Nurr1-RXRα agonists was essential for elucidating the LBD heterodimer dissociation mechanism. Together, our findings highlight the importance of using a more functionally diverse RXR ligand set to define the mechanism of Nur77-RXRγ activation and to further evaluate whether LBD heterodimer dissociation represents a shared activation mechanism among NR4A-RXR heterodimers relevant to neurodegenerative and inflammatory diseases.

Unbend, correction of local beam-induced sample motion in cryo-EM images using a 3D spline model

lingli.kong1@umassmed.edu (Johannes Elferich) — Thu, 30 Apr 2026 00:00:00 +0000

The exposure of frozen biological samples to the high-energy electron beam in a cryo-electron microscope commonly leads to beam-induced sample motion and distortions. Previously, we described Unblur, software to correct for beam-induced motion based on the alignment of full frames in a movie collected during the beam exposure (Grant and Grigorieff, 2015). Here, we present Unbend, extending Unblur by accommodating more localized sample bending and distortions using a 3D cubic B-spline model. Unbend is integrated into our cisTEM software with a new local motion visualization panel. We processed movie frames from various in situ sample types, including whole cells, lamellae, and cell lysates, to analyze motion behavior across different specimen types. To quantify the improvement in high-resolution signal, we utilized the 2D template matching method to search large ribosomal subunits from the motion-corrected micrographs. Overall, the signal-to-noise ratio of detected particles improved by 3–8% across different samples compared with full-frame aligned micrographs, while the number of detected target particles increased by up to ~300%. Furthermore, we processed micrograph montages to study motion patterns across an entire sample, revealing considerable variance in distortion scale within the same sample, suggesting a complex underlying mechanism.

Interrogating the structure and function of the human voltage-gated proton channel (hH_v1) with a fluorescent noncanonical amino acid

zagotta@uw.edu (Emerson M Carmona) — Tue, 28 Apr 2026 00:00:00 +0000

The human voltage-gated proton channel (hH_v1) is a dimer of voltage-sensor domains (VSDs) containing highly selective proton permeation pathways in each monomer. In addition to voltage, hH_v1 is regulated by other stimuli, including pH gradients, mechanical forces, and ligands, such as Zn²⁺. Aside from the VSDs, this membrane protein contains an N-terminal domain and a C-terminal coiled-coil domain (CC) formed between the monomers. To address the need for direct measurements of conformational rearrangements in hH_v1, we developed a Förster resonance energy transfer (FRET) approach to measuring the conformational rearrangements in full-length hH_v1 purified from E. coli. We used genetic code expansion (GCE) to generate a library of 14 full-length hH_v1 constructs, each incorporating the fluorescent noncanonical amino acid acridon-2-ylalanine (Acd) at a different site throughout the various structural domains. Following the expression and purification of these hH_v1-Acd proteins, we found that 12 sites yielded stable and functional proton-permeable channels. The fluorescence properties of Acd at each site showed small site-specific differences. Furthermore, we measured site-specific FRET efficiencies from tryptophan (Trp) and tyrosine (Tyr) to Acd in the hH_v1-Acd proteins and found results consistent with correct folding in detergent micelles. Finally, the addition of Zn²⁺ produced reversible changes in FRET, with affected residues clustered on the intracellular side of the channel.

Distinct mechanisms of inhibition of Kv2 potassium channels by tetraethylammonium and RY785

jfg4wrk@gmail.com (Esam A Orabi) — Mon, 27 Apr 2026 00:00:00 +0000

Voltage-gated K⁺ channels play central roles in human physiology, in health, and disease. A repertoire of inhibitors that are both potent and specific would, therefore, be of great value. RY785 has been described as promising in this regard, as it selectively inhibits channels in the Kv2 subfamily with high potency. Its mechanism of action has not yet been determined at the molecular level, but functional studies indicate it differs from those of less specific inhibitors, such as quaternary-ammonium compounds or aminopyridines. To examine this mechanism at the single-molecule level, we have carried out a series of all-atom molecular dynamics simulations based on the structure of the Kv2.1 channel in the ion-conducting state. The simulations demonstrate both RY785 and tetraethylammonium spontaneously enter the channel interior through the cytoplasmic gate, but with distinct effects. Tetraethylammonium binds to a site adjacent to the selectivity filter, on the pore axis, thus blocking the flow of K⁺ ions. RY785, by contrast, binds to the channel walls, off-axis, and allows K⁺ flow while the gate remains open. This observation indicates RY785 inhibits Kv2.1 by fostering the occlusion of the gate, through a network of hydrophobic interactions therein, explaining why it also modulates the voltage-sensing mechanism of the channel, 3 nanometers away.

SMC complex unidirectionally translocates DNA by coupling segment capture with an asymmetric kleisin path

takada@biophys.kyoto-u.ac.jp (Giovanni Bruno Brandani) — Wed, 22 Apr 2026 00:00:00 +0000

SMC (structural maintenance of chromosomes) protein complexes are ring-shaped molecular motors essential for genome folding. Despite recent progress, the detailed molecular mechanism of DNA translocation in concert with the ATP-driven conformational changes of the complex remains to be clarified. In this study, we elucidated the mechanisms of SMC action on DNA using all-atom and coarse-grained molecular dynamics simulations. We first created a near-atomic full-length model of a prokaryotic SMC–kleisin complex based on experimental structures and implemented ATP-dependent conformational changes using a structure-based coarse-grained model. We further incorporated key protein–DNA hydrogen-bond interactions derived from fully atomistic simulations. Extensive simulations of the SMC complex with 800 base pairs of duplex DNA over the ATP cycle observed unidirectional DNA translocation by the SMC complex. The process exhibited a step size of ~200 base pairs, wherein the SMC complex captured a DNA segment of about the same size within the SMC ring in the engaged state, followed by its pumping into the kleisin ring as ATP was hydrolyzed. Analysis of trajectories identified the asymmetric path of the kleisin as a critical factor for the observed unidirectionality.

PPIscreenML is a method for structure-based screening of protein-protein interactions using AlphaFold

johnkaranicolas1@gmail.com (Jesse Chen) — Tue, 21 Apr 2026 00:00:00 +0000

Protein-protein interactions underlie nearly all cellular processes. With the advent of protein structure prediction methods such as AlphaFold2 (AF2), models of specific protein pairs can be built extremely accurately in most cases. However, determining the relevance of a given protein pair remains an open question. It is presently unclear how to use best structure-based tools to infer whether a pair of candidate proteins indeed interacts with one another: ideally, one might even use such information to screen among candidate pairings to build up protein interaction networks. Whereas methods for evaluating quality of modeled protein complexes have been co-opted for determining which pairings interact (e.g. pDockQ and iPTM), there have been no rigorously benchmarked methods for this task. Here, we introduce PPIscreenML, a classification model trained to distinguish AF2 models of interacting protein pairs from AF2 models of compelling decoy pairings. We find that PPIscreenML outperforms methods such as pDockQ and iPTM for this task, and further that PPIscreenML exhibits impressive performance when identifying which ligand/receptor pairings engage one another across the structurally conserved tumor necrosis factor superfamily (TNFSF). Analysis of benchmark results using complexes not seen in PPIscreenML development strongly suggests that the model generalizes beyond training data, making it broadly applicable for identifying new protein complexes based on structural models built with AF2.

Structural mechanisms of pump assembly and drug transport in the AcrAB–TolC efflux system

gxf16@tsinghua.org.cn (Jiawei Wang) — Mon, 20 Apr 2026 00:00:00 +0000

Tripartite multidrug efflux pumps that span the cell envelope are essential for antibiotic resistance in Gram-negative bacteria. Here, we report cryo-EM structures of two endogenous efflux complexes from Escherichia coli: a TolC–YbjP subcomplex at 3.56 Å resolution and the complete TolC–YbjP–AcrABZ pump at 3.39 Å. Structural analysis reveals that YbjP, a previously uncharacterized lipoprotein, binds TolC in a 3:3 stoichiometry, bridging the TolC protomers at their equatorial domain. Clear density of the mature YbjP’s N-terminal Cys19 indicates that YbjP is anchored to the outer membrane by an N-terminal lipid moiety. Notably, YbjP remains bound as TolC undergoes AcrA-induced opening, suggesting that this accessory protein accommodates the conformational change. The AcrB trimer simultaneously presents three distinct conformational states (L, T, and O), capturing a complete transport cycle. These high-resolution structures provide insights into the architecture and mechanism of clinically relevant efflux machinery, identifying YbjP as a previously unrecognized structural component that contributes to TolC positioning, and may assist in its membrane localization.

A lipoprotein partner for the Escherichia coli outer membrane protein TolC

bfl20@cam.ac.uk (Andrzej Harris) — Wed, 15 Apr 2026 00:00:00 +0000

The outer membrane protein TolC from Escherichia coli belongs to an extensive superfamily whose members are found throughout the didermal, Gram-negative bacterial lineages. The protein serves as an activated exit duct in multi-drug efflux pumps and protein secretion machinery. Many TolC homologues bear a lipid modification on the N-terminus that embeds into the inner leaflet of the outer membrane and appears to have been a conserved feature; however, the moiety is absent entirely in the E. coli TolC. We have discovered that the E. coli lipoprotein YbjP interacts extensively with the periplasmic surface of TolC and its N-terminal lipid moiety is embedded in the membrane, mimicking the intramolecular and modification-membrane interactions seen in TolC homologues. Here, we present cryo-EM structures of the MacA-MacB-TolC and AcrA-AcrB-TolC tripartite pumps complexed to YbjP. Although the association occurs spontaneously both in vitro and in vivo, the YbjP-TolC interaction is not required for efflux activity under standard laboratory conditions. YbjP may contribute to stabilising the orientation and distribution of TolC in the outer membrane, as well as the expression of transporters for tryptophan and cyclic peptide toxins.

Active regulation of the epidermal growth factor receptor by the membrane bilayer

binz@mit.edu (Bin Zhang) — Tue, 14 Apr 2026 00:00:00 +0000

Cell surface receptors transmit information across the plasma membrane to connect the extracellular environment to intracellular function. While the structures and interactions of the receptors have been long established as mediators of signaling, increasing evidence suggests that the membrane itself plays an active role in both suppressing and enhancing signaling. Identifying and investigating this contribution has been challenging owing to the complex composition of the plasma membrane. We used cell-free expression to incorporate the epidermal growth factor receptor (EGFR) into nanodiscs with defined membrane compositions and characterized ligand-induced transmembrane conformational response and interactions with signaling partners using single-molecule and ensemble fluorescence assays. We observed that both the transmembrane conformational response and interactions with signaling partners are strongly lipid dependent, consistent with previous observations of electrostatic interactions between the anionic lipids and conserved basic residues near the membrane adjacent domain. Strikingly, the active conformation of EGFR and high levels of ATP binding were maintained regardless of ligand binding with high anionic lipid content typical of cancer cells, where EGFR signaling is enhanced. In contrast, the conformational response was suppressed in the presence of cholesterol, providing a mechanism for its known inhibitory effect on EGFR signaling. Our findings introduce a model of EGFR signaling in which the lipid environment can override ligand control, providing a biophysical basis for both robust EGFR activity in healthy cells and aberrant activity under pathological conditions. The membrane-adjacent protein sequence, likely responsible for the lipid dependence, is conserved among receptor tyrosine kinases, suggesting that active regulation by the plasma membrane may be a general feature of this important class of proteins.

A structural code for assembly specificity in GID/CTLH-type E3 ligases

hermann.schindelin@virchow.uni-wuerzburg.de (Hermann Schindelin) — Wed, 08 Apr 2026 00:00:00 +0000

GID/CTLH-type E3 ligases assemble into conserved ring-shaped architectures built from repeating LisH-CTLH-CRA modules, yet the molecular rules that enforce their highly specific subunit arrangement have remained unknown. Here, we decode the structural ‘assembly specificity code’ that governs CRA-CRA pairing. Using crystal structures of multiple CTLH-CRA domains, including the RanBP9-muskelin heterodimer, integrated with quantitative binding analyses, we show that several interfaces operate with exceptionally high affinity, reaching the picomolar range, and that conserved sequence and geometric features enable each subunit to only select cognate partners. Strikingly, targeted perturbations of these features are sufficient to reprogram pairing preferences, enabling engineered subunits such as RanBP10 or Twa1 to adopt non-native interaction partners. These findings reveal the molecular logic that preserves the architecture of GID/CTLH-type E3 ligases and demonstrate that their assembly code is both decipherable and engineerable, providing a conceptual foundation for reconfiguring these ring-shaped E3 ligases.

How enzymes make the right choice during biosynthesis

camilo.perez@uga.edu (Ana S Ramírez) — Wed, 08 Apr 2026 00:00:00 +0000

The biosynthesis of an important biopolymer called hyaluronan requires an enzyme that discriminates between two different substrates.

Detecting directed motion and confinement in single-particle trajectories using hidden variables

simon.francois@protonmail.com (Caroline Boudoux) — Tue, 07 Apr 2026 00:00:00 +0000

Single-particle tracking is a powerful tool for understanding protein dynamics and characterizing microenvironments. As the motion of unconstrained nanoscale particles is governed by Brownian diffusion, deviations from this behavior are biophysically insightful. However, the stochastic nature of particle movement and the presence of localization error pose a challenge for the robust classification of non-Brownian motion. Here, we present aTrack, a versatile tool for classifying track behaviors and extracting key parameters for particles undergoing Brownian, confined, or directed motion. Our tool quickly and accurately estimates motion parameters from individual tracks. Further, our tool can analyze populations of tracks and determine the most likely number of motion states. We show the working range of our approach on simulated tracks and demonstrate its application for characterizing particle motion in Saccharomyces cerevisiae and for biosensing applications in Escherichia coli. aTrack is implemented as a stand-alone software, making it simple to analyze track data.

Transforming a fragile protein helix into an ultrastable scaffold via a hierarchical AI and chemistry framework

pengz@nju.edu.cn (Bin Zheng) — Thu, 02 Apr 2026 00:00:00 +0000

The rational design of proteins that maintain structural integrity under concurrent thermal, mechanical, and chemical stress remains a challenge in molecular engineering. We present a hierarchical framework that transforms an α-helical domain into an ultrastable scaffold by integrating AI-guided design with foundational chemical principles. This approach progresses from global architectural reinforcement, using multiple AI tools to create a stabilized four-helix bundle, to local chemical tuning, where AlphaFold3 guides the installation of salt bridges and metal-coordination motifs. A computational pipeline using physics-based screening such as molecular dynamics simulations efficiently distilled millions of designs into a minimal candidate set. The resulting α-helical proteins exhibit unprecedented multi-axis stability, with mechanical unfolding forces exceeding 200 pN, thermal resilience>100°C, and high resistance to chemical denaturants. By systematically dissecting the contributions of hydrophobic packing, electrostatics, and metal coordination, we establish a general blueprint for imparting extreme robustness. This work bridges AI-driven structural generation with chemical precision, advancing the creation of durable proteins for mechanistic studies and synthetic biology.

Two binding sites are better than one

jeburke@uvic.ca (John E Burke) — Wed, 01 Apr 2026 00:00:00 +0000

The reasons why two multiprotein complexes – VPS34 complex I and VPS34 complex II – are activated by different Rab proteins are becoming clearer.

A missing link for efflux pumps

isabelle.broutin@parisdescartes.fr (Hilal Wehbi) — Wed, 25 Mar 2026 00:00:00 +0000

A lipoprotein called YbjP could be the answer to a puzzle about efflux pumps in gram-negative bacteria.

Adaptor protein supersaturation drives innate immune signaling and cell fate

rhn@stowers.org (Alejandro Rodriguez Gama) — Tue, 24 Mar 2026 00:00:00 +0000

How minute pathogenic signals trigger decisive immune responses is a fundamental question in biology. Classical signaling often relies on ATP-driven enzymatic cascades, but innate immunity frequently employs death fold domain (DFD) self-assembly. The energetic basis of this assembly is unknown. Here, we show that specific DFDs function as energy reservoirs through metastable supersaturation. Characterizing all 109 human DFDs, we identified sequence-encoded nucleation barriers specifically in the central adaptors of inflammatory signalosomes, allowing them to accumulate far above their saturation concentration while remaining soluble and poised for activation. We demonstrate that the inflammasome adaptor ASC is constitutively supersaturated in vivo, retaining energy that powers on-demand cell death. Swapping a non-supersaturable DFD in the apoptosome with a supersaturable one sensitized cells to sublethal stimuli. Mapping all DFD nucleating interactions revealed that supersaturated adaptors are triggered to polymerize specifically by other DFDs in their respective pathways, limiting potentially deleterious crosstalk. Across human cell types, adaptor supersaturation strongly correlates with cell turnover, implicating this thermodynamic principle in the trade-off between immunity and longevity. Profiling homologues from fish and sponge, we find nucleation barriers to be conserved across metazoa. These findings reveal DFD adaptors as biological phase change materials in thermal batteries to power cellular life-or-death decisions on demand.

Insights into substrate binding and utilization by hyaluronan synthase

jz3x@virginia.edu (Jochen Zimmer) — Fri, 13 Mar 2026 00:00:00 +0000

Hyaluronan (HA), a heteropolysaccharide of alternating N-acetylglucosamine (GlcNAc) and glucuronic acid (GlcA), is an essential component of the vertebrate extracellular matrix. HA biosynthesis proceeds via three evolutionarily convergent reaction mechanisms, catalyzed by the membrane-integrated class 1 enzymes that either elongate the non-reducing (NR) or reducing end of HA, as well as the class 2 hyaluronan synthase (HAS), a soluble non-processive enzyme. Class 1-NR HAS, found in both vertebrates and large double-stranded DNA viruses, is monomeric and couples HA polymerization via coordinated transfer of UDP-GlcNAc and UDP-GlcA substrates with the secretion of the nascent HA chain through its own transmembrane channel. How this HAS discriminates between two UDP-sugars using a single active site is a critical, yet unresolved question. Using single-particle cryo-EM, we reveal a two-step process by which the Chlorella virus HAS (CvHAS) recognizes and positions its substrate, UDP-GlcA, for glycosyl transfer. Further, we report greatly diminished turnover of UDP-GlcA in the absence of a primer, distinguishing acceptor-free activity toward UDP-GlcNAc. Lastly, prompted by observation of a dodecyl maltoside bound HAS, we demonstrate the utility of non-canonical acceptors in priming of a UDP-GlcA transfer reaction. Altogether, this work clarifies the molecular basis for HAS’ dual substrate specificity and the role of UDP-GlcA recognition in integrity of HA synthesis.

Multiple modes of cholesterol translocation in the human Smoothened receptor

diwakar@illinois.edu (Diwakar Shukla) — Wed, 11 Mar 2026 00:00:00 +0000

Smoothened (SMO), a member of the G-protein-coupled receptor superfamily, mediates Hedgehog signaling and is linked to cancer and birth defects. SMO responds to accessible cholesterol in the ciliary membrane, translocating it via a longitudinal tunnel to its extracellular domain. Reaching a complete mechanistic understanding of the cholesterol translocation process would help in the development of cancer therapies. Experimental data suggest two modes of translocation to support entry of cholesterol from outer and inner membrane leaflets, but the exact mechanism of translocation remains unclear. Using atomistic molecular dynamics simulations (∼2 ms simulations) and biochemical assays of SMO mutants, we assess the energetic feasibilities of the two modes. We show that the highest energetic barrier for cholesterol translocation from the outer leaflet is lower than that from the inner leaflet. Mutagenesis experiments and complementary simulations of SMO mutants validate the role of critical amino acid residues along the translocation pathways. Our data suggests that cholesterol can take either pathway to enter SMO, thus explaining experimental observations in the literature. Thus, our results illuminate the energetics and provide a first molecular description of cholesterol translocation in SMO.

Protein-induced membrane strain drives supercomplex formation

ville.kaila@dbb.su.se (Alexander Jussupow) — Mon, 23 Feb 2026 00:00:00 +0000

Mitochondrial membranes harbor the electron transport chain (ETC) that powers oxidative phosphorylation (OXPHOS) and drives the synthesis of ATP. Yet, under physiological conditions, the OXPHOS proteins operate as higher-order supercomplex (SC) assemblies, although their functional role remains poorly understood and much debated. By combining large-scale atomistic and coarse-grained molecular simulations with analysis of cryo-electron microscopic data and statistical as well as kinetic models, we show here that the formation of the mammalian I/III₂ supercomplex reduces the molecular strain of inner mitochondrial membranes by altering the local membrane thickness and leading to an accumulation of both cardiolipin and quinone around specific regions of the SC. We find that the SC assembly also affects the global motion of the individual ETC proteins with possible functional consequences. On a general level, our findings suggest that molecular crowding and strain effects provide a thermodynamic driving force for the SC formation, with a possible flux enhancement in crowded biological membranes under constrained respiratory conditions.

Structure of the human CTF18−RFC clamp loader bound to PCNA

samir.hamdan@kaust.edu.sa (Alfredo De Biasio) — Mon, 23 Feb 2026 00:00:00 +0000

Sliding clamps like PCNA are crucial processivity factors for replicative polymerases, requiring specific clamp loaders for loading onto DNA. The human alternative clamp loader CTF18–RFC interacts with the leading strand polymerase Pol ε and loads PCNA onto primer/template DNA using its RFC pentameric module. Here, we provide a structural characterization of the human CTF18–RFC complex and its interaction with PCNA. Our cryo-EM data support that the Ctf8 and Dcc1 subunits of CTF18–RFC, which form the regulatory module interacting with Pol ε, are flexibly tethered to the RFC module. A 2.9 Å cryo-EM structure shows the RFC module bound to PCNA in an autoinhibited conformation similar to the canonical RFC loader, marking the initial step of the clamp-loading reaction. The unique RFC1 (Ctf18) large subunit of CTF18–RFC, which based on the cryo-EM map shows high relative flexibility, is anchored to PCNA through an atypical low-affinity PIP box in the AAA+ domain and engages the RFC5 subunit using a novel β-hairpin at the disordered N-terminus. We show that deletion of this β-hairpin impairs the CTF18–RFC−PCNA complex stability, slows down clamp loading, and decreases the rate of primer synthesis by Pol ε. Our research identifies distinctive structural characteristics of the human CTF18–RFC complex, providing insights into its role in PCNA loading and the stimulation of leading strand synthesis by Pol ε.

Accessibility of the unstructured α-tubulin C-terminal tail is controlled by microtubule lattice conformation

oryoma@umich.edu (David Sept) — Mon, 09 Feb 2026 00:00:00 +0000

Microtubules are cytoskeletal filaments that self-assemble from the protein tubulin, a heterodimer of α-tubulin and β-tubulin, and are important for cell mechanics, migration, and division. Much work has focused on how the nucleotide state of β-tubulin regulates the structure and dynamics of microtubules. In contrast, less is known about the structure and function of the C-terminal tails (CTTs) of α- and β-tubulin which are thought to freely protrude from the surface of the microtubule. To study the CTT of α-tubulin, we developed three different biosensors that bind the tyrosinated α-tubulin CTT (Y-αCTT). Surprisingly, live imaging of the probes indicates that the Y-αCTT is minimally accessible along the microtubule lattice under normal cellular conditions. Lattice binding of the Y-αCTT probes can be increased by three different ways of changing the tubulin conformational state: the drug Taxol, expression of microtubule-associated proteins (MAPs) that recognize or promote an expanded tubulin conformation, or expression of tubulin that cannot hydrolyze GTP. Molecular dynamics simulations indicate that the Y-αCTT undergoes numerous transient interactions with the bodies of α-tubulin and β-tubulin in the lattice, and that the frequency of these interactions is regulated by the tubulin nucleotide state. These findings suggest that accessibility of the Y-αCTT is locally governed by nucleotide- and MAP-dependent conformational changes to tubulin subunits within the microtubule lattice.

Lipids challenge ligands to control receptors

adam.wollman@newcastle.ac.uk (Adam JM Wollman) — Wed, 04 Feb 2026 00:00:00 +0000

The behaviour of a receptor protein can be influenced by the presence of certain lipids in the membrane it is embedded in.

MRI sets its sights on collagen

fritz.schick@med.uni-tuebingen.de (Fritz Schick) — Mon, 02 Feb 2026 00:00:00 +0000

Reducing the echo time of a whole-body MRI scanner makes it possible to image collagen, an important structural protein found in bones and tendons.

Cryo-EM structure revealed a novel F-actin binding motif in a Legionella pneumophila lysine fatty acyltransferase

ym253@cornell.edu (Garrison Komaniecki) — Wed, 28 Jan 2026 00:00:00 +0000

Legionella pneumophila is an opportunistic bacterial pathogen that causes Legionnaires’ disease. To establish an intracellular niche conducive to replication, L. pneumophila translocates a diverse array of effector proteins that manipulate various host cellular processes, including the actin cytoskeleton. In a screen for effectors that alter actin dynamics, we identified a Legionella effector, Lfat1 (lpg1387), which colocalizes with the actin cytoskeleton in eukaryotic cells. Lfat1 specifically binds F-actin through a novel actin-binding domain (ABD). High-resolution cryo-electron microscopy (Cryo-EM) analysis revealed that this ABD forms a long α-helix hairpin, with its tip interacting with subdomains I and II of two adjacent actin molecules within the F-actin filament. Interestingly, while individual α-helices of the hairpin fail to bind F-actin, co-expression as separate fusion proteins restores binding activity. Furthermore, we demonstrated that Lfat1 exhibits lysine fatty acyltransferase (KFAT) activity, targeting host small GTPases. These findings establish a foundation for studying the KFAT family of bacterial toxins and uncover a novel F-actin-binding motif, providing an alternative F-actin marker with notable flexibility.

Allosteric effects of the coupling cation in melibiose transporter MelB

lan.guan@ttuhsc.edu (Amirhossein Bakhtiiari) — Wed, 28 Jan 2026 00:00:00 +0000

The major facilitator superfamily (MFS) transporters play significant roles in human health and disease. Salmonella enterica serovar Typhimurium melibiose permease (MelB_St) catalyzes the symport of galactosides with Na⁺, H⁺, or Li⁺ and is a prototype of MFS transporters. We published the structures of MelB_St in both inward- and outward-facing conformations, bound to galactoside or Na⁺, and proposed that positive cooperativity of the co-transported solutes is crucial for the symport mechanism. Here, we elucidated the underlying mechanisms by analyzing MelB_St dynamics and the effects of melibiose, Na⁺, or both using hydrogen-deuterium exchange mass spectrometry (HDX-MS). We also refined the determinants of sugar recognition by solving the crystal structures of a uniporter D59C MelB_St complexed with melibiose and other sugars, and by identifying a critical water molecule involved in sugar recognition. Our integrated studies, combining structures, HDX-MS, and molecular dynamics simulations, support the conclusion that sugar-binding affinity is directly correlated with protein dynamics. Na⁺ acts as an allosteric activator, reducing the flexibility of dynamic residues in the sugar-binding site and in the cytoplasmic gating salt-bridge network, thereby increasing sugar-binding affinity. This study provides a molecular-level framework of the symport mechanism that could serve as a general model for cation-coupled symporters.

Ω-Loop mutations control dynamics of the active site by modulating the hydrogen-bonding network in PDC-3 β-lactamase

shozeb.haider@ucl.ac.uk (Andrea M Hujer) — Wed, 21 Jan 2026 00:00:00 +0000

The expression of antibiotic-inactivating enzymes, such as Pseudomonas-derived cephalosporinase-3 (PDC-3), is a major mechanism of intrinsic resistance in bacteria. Using reinforcement learning-driven molecular dynamics simulations and constant pH MD, we investigate how clinically observed mutations in the Ω-loop (at residues V211, G214, E219, and Y221) alter the structure and function of PDC-3. Our findings reveal that these substitutions modulate the dynamic flexibility of the Ω-loop and the R2-loop, reshaping the cavity of the active site. In particular, E219K and Y221A disrupt the tridentate hydrogen bond network around K67, thus lowering its pKa and promoting proton transfer to the catalytic residue S64. Markov state models reveal that E219K achieves enhanced catalysis by adopting stable, long-lived ‘active’ conformations, whereas Y221A facilitates activity by rapidly toggling between bond-formed and bond-broken states. In addition, substitutions influence key hydrogen bonds that control the opening and closure of the active-site pocket, consequently influencing the overall size. The pocket expands in all nine clinically identified variants, creating additional space to accommodate bulkier R1 and R2 cephalosporin side chains. Taken together, these results provide a mechanistic basis for how single residue substitutions in the Ω-loop affect catalytic activity. Insights into the structural dynamics of the catalytic site advance our understanding of emerging β-lactamase variants and can inform the rational design of novel inhibitors to combat drug-resistant P. aeruginosa.