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Glu-311 in External Loop 4 of the Sodium/Proline Transporter PutP Is Crucial for External Gate Closure


The available structural information on LeuT and structurally related transporters suggests that external loop 4 (eL4) and the outer end of transmembrane domain (TM) 10' participate in the reversible occlusion of the outer pathway to the solute binding sites. Here, the functional significance of eL4 and the outer region of TM10' are explored using the sodium/proline symporter PutP as a model. Glu-311 at the tip of eL4, and various amino acids around the outer end of TM10' are identified as particularly crucial for function. Substitutions at these sites inhibit the transport cycle, and affect in part ligand binding. In addition, changes at selected sites induce a global structural alteration in the direction of an outward-open conformation. It is suggested that interactions between the tip of eL4 and the peptide backbone at the end of TM10' participate in coordinating conformational alterations underlying the alternating access mechanism of transport. Together with the structural information on LeuT-like transporters, the results further specify the idea that common design and functional principles are maintained across different transport families.

Type Journal
ISBN 1083-351X (Electronic) 0021-9258 (Linking)
Authors Bracher, S. ; Guerin, K. ; Polyhach, Y. ; Jeschke, G. ; Dittmer, S. ; Frey, S. ; Bohm, M. ; Jung, H.;
Published Date 2016-01-01
Published Volume 291
Published Issue 10
Published Pages 4998-5008
Status Published in-print
URL link to publisher's version
OpenAccess link to author's accepted manuscript version