Revealing an outward-facing open conformational state in a CLC Cl-/H+ exchange transporter
- Stanford University School of Medicine, United States
- University of Illinois at Urbana-Champaign, United States
- Stanford University, United States
- Vanderbilt University, United States
Abstract
CLC secondary active transporters exchange Cl- for H+. Crystal structures have suggested that the conformational change from occluded to outward-facing states is unusually simple, involving only the rotation of a conserved glutamate (Gluex) upon its protonation. Using 19F NMR, we show that as [H+] is increased to protonate Gluex and enrich the outward-facing state, a residue ~20 Å away from Gluex, near the subunit interface, moves from buried to solvent-exposed. Consistent with functional relevance of this motion, constriction via inter-subunit cross-linking reduces transport. Molecular dynamics simulations indicate that the cross-link dampens extracellular gate-opening motions. In support of this model, mutations that decrease steric contact between Helix N (part of the extracellular gate) and Helix P (at the subunit interface) remove the inhibitory effect of the cross-link. Together, these results demonstrate the formation of a previously uncharacterized 'outward-facing open' state, and highlight the relevance of global structural changes in CLC function.
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© 2016, Khantwal et al.
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Revealing an outward-facing open conformational state in a CLC Cl-/H+ exchange transporter
eLife 5:e11189.
https://doi.org/10.7554/eLife.11189
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