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Title: Revealing an outward-facing open conformational state in a CLC Cl /H + exchange transporter

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 (Glu ex ) upon its protonation. Using 19 F NMR, we show that as [H + ] is increased to protonate Glu ex and enrich the outward-facing state, a residue ~20 Å away from Glu ex , 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.
Authors:
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Publication Date:
OSTI Identifier:
1237979
Grant/Contract Number:
AC02-76SF00515
Type:
Published Article
Journal Name:
eLife
Additional Journal Information:
Journal Volume: 5; Journal ID: ISSN 2050-084X
Publisher:
eLife Sciences Publications, Ltd.
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English