Binding and sequestration of poison frog alkaloids by a plasma globulin
- Stanford University, United States
- Leibniz Institute for the Analysis of Biodiversity Change, Germany
- Centro Jambatu de Investigación y Conservación de Anfibios, Ecuador
Abstract
Alkaloids are important bioactive molecules throughout the natural world, and in many animals they serve as a source of chemical defense against predation. Dendrobatid poison frogs bioaccumulate alkaloids from their diet to make themselves toxic or unpalatable to predators. Despite the proposed roles of plasma proteins as mediators of alkaloid trafficking and bioavailability, the responsible proteins have not been identified. We use chemical approaches to show that a ~50 kDa plasma protein is the principal alkaloid binding molecule in blood of poison frogs. Proteomic and biochemical studies establish this plasma protein to be a liver-derived alkaloid-binding globulin (ABG) that is a member of the serine-protease inhibitor (serpin) family. In addition to alkaloid binding activity, ABG sequesters and regulates the bioavailability of “free” plasma alkaloids in vitro. Unexpectedly, ABG is not related to saxiphilin, albumin, or other known vitamin carriers, but instead exhibits sequence and structural homology to mammalian hormone carriers and amphibian biliverdin binding proteins. Alkaloid-binding globulin (ABG) represents a new small molecule binding functionality in serpin proteins, a novel mechanism of plasma alkaloid transport in poison frogs, and more broadly points towards serpins acting as tunable scaffolds for small molecule binding and transport across different organisms.
Data availability
All raw data, analysis scripts, and intermediate data analysis are available either as Source Data zip files for each figure, or through public repositories. Uncropped gel images, analysis and plotting code, raw and normalized MST data, normalized RNAseq data, and other intermediate analysis files used to make figures are available as "Source Data" zip files included with the submission. All raw proteomics and mass spectrometry data are available on DataDryad: https://doi.org/10.5061/dryad.mkkwh7143. The official ABG sequences can be found through GenBank with the following accessions: O. sylvatica (OQ032869), D. tinctorius (OQ032870), and E. tricolor (OQ032871). The O. sylvatica genome, field collected sample information, raw and trimmed sequencing reads are available through the NCBI BioProject PRJNA909817. The A. femoralis genome and raw sequencing data is available through NCBI BioProject PRJNA913987. Annotated versions of the A. femoralis and O. sylvatica genomes, as well as E. tricolor, D. tinctorius, and M. aurantiaca transcriptomes are available on DataDryad: https://doi.org/10.5061/dryad.mkkwh7143.
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Binding and sequestration of poison frog alkaloids by a plasma globulinDryad Digital Repository, doi:10.5061/dryad.mkkwh7143.
Article and author information
Author details
Aurora Alvarez-Buylla
Lauren A O'Connell
Funding
National Science Foundation (IOS-1822025)
- Lauren A O'Connell
New York Stem Cell Foundation
- Lauren A O'Connell
National Science Foundation Graduate Research Fellowship Program (DGE-1656518)
- Aurora Alvarez-Buylla
Howard Hughes Medical Institute (GT13330)
- Aurora Alvarez-Buylla
Fundacion Alfonso Martin Escudero
- Maria Dolores Moya Garzon
Wu Tsai Human Performance Alliance
- Maria Dolores Moya Garzon
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Animal experimentation: All animal procedures were approved by the Institutional Animal Care and Use Committee at Stanford (protocol #34153). Topical benzocaine was used for anesthesia prior to the euthanasia of all animals. Laboratory-bred animals were purchased from Understory Enterprises (Ontario, Canada) or Josh's Frogs (Michigan, USA) depending on the species. Animals were either euthanized for plasma collection upon arrival, or housed in 183 inch glass terraria, and fed a diet of non-toxic Drosophila melanogaster until euthanasia. Plasma and tissues from a total of 62 animals were used for this study, consisting of 32 lab-bred animals and 30 field-collected animals that are described below. Sample size of field-collected animals was determined based on variability seen in previous studies, and for laboratory experiments based on experimental needs in terms of volume of plasma.
Copyright
© 2023, Alvarez-Buylla et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Binding and sequestration of poison frog alkaloids by a plasma globulin
eLife 12:e85096.
https://doi.org/10.7554/eLife.85096
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