Extracellular Loop 4 of the Proline Transporter PutP Controls the Periplasmic Entrance to Ligand Binding Sites

Autor(en): Raba, Michael
Dunkel, Sabrina
Hilger, Daniel
Lipiszko, Kamila
Polyhach, Yevhen
Jeschke, Gunnar
Bracher, Susanne
Klare, Johann P.
Quick, Matthias
Jung, Heinrich
Steinhoff, Heinz-Juergen 
Stichwörter: BACTERIAL HOMOLOG; Biochemistry & Molecular Biology; Biophysics; Cell Biology; CONFORMATIONAL-CHANGES; CRYSTAL-STRUCTURE; DISTANCE MEASUREMENTS; ESCHERICHIA-COLI; MEMBRANE-TRANSPORT; MOLECULAR-BASIS; NA+/PROLINE TRANSPORTER; PROTEIN-STRUCTURE; TRANSMEMBRANE DOMAIN-IX
Erscheinungsdatum: 2014
Herausgeber: CELL PRESS
Journal: STRUCTURE
Volumen: 22
Ausgabe: 5
Startseite: 769
Seitenende: 780
Zusammenfassung: 
The Na+/proline symporter (PutP), like several other Na+-coupled symporters, belongs to the so-called LeuT-fold structural family, which features ten core transmembrane domains (cTMs) connected by extra- and intracellular loops. The role of these loops has been discussed in context with the gating function in the alternating access model of secondary active transport processes. Here we report the complete spin-labeling site scan of extracellular loop 4 (eL4) in PutP that reveals the presence of two alpha-helical segments, eL4a and eL4b. Among the eL4 residues that are directly implicated in the functional dynamics of the transporter, Phe314 in eL4b anchors the loop by means of hydrophobic contacts to cTM1 close to the ligand binding sites. We propose that ligand-induced conformational changes at the binding sites are transmitted via the anchoring residue to eL4 and through eL4 further to adjacent cTMs, leading to closure of the extracellular gate.
ISSN: 09692126
DOI: 10.1016/j.str.2014.03.011

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