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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:
 [1] ;  [1] ;  [2] ;  [2] ;  [1] ;  [1] ;  [1] ;  [3] ;  [4] ;  [5] ;  [5] ;  [2] ;  [1]
  1. Stanford Univ. School of Medicine, Stanford, CA (United States)
  2. Univ. of Illinois, Urbana, IL (United States)
  3. Stanford Univ. School of Medicine, Stanford, CA (United States). Stanford Magnetic Resonance Laboratory
  4. Stanford Univ., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
  5. Vanderbilt Univ., Nashville, TN (United States)
Publication Date:
Grant/Contract Number:
AC02-76SF00515; MCA06N060
Type:
Published Article
Journal Name:
eLife
Additional Journal Information:
Journal Volume: 5; Journal ID: ISSN 2050-084X
Publisher:
eLife Sciences Publications, Ltd.
Research Org:
Stanford Univ., CA (United States). School of Medicine
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1237979
Alternate Identifier(s):
OSTI ID: 1237980; OSTI ID: 1254484