title: Structural basis for the facilitative diffusion mechanism by SemiSWEET transporter.
abstract: SWEET family proteins mediate sugar transport across biological membranes and play crucial roles in plants and animals. The SWEETs and their bacterial homologues, the SemiSWEETs, are related to the PQ-loop family, which is characterized by highly conserved proline and glutamine residues (PQ-loop motif). Although the structures of the bacterial SemiSWEETs were recently reported, the conformational transition and the significance of the conserved motif in the transport cycle have remained elusive. Here we report crystal structures of SemiSWEET from Escherichia coli, in the both inward-open and outward-open states. A structural comparison revealed that SemiSWEET undergoes an intramolecular conformational change in each protomer. The conserved PQ-loop motif serves as a molecular hinge that enables the 'binder clip-like' motion of SemiSWEET. The present work provides the framework for understanding the overall transport cycles of SWEET and PQ-loop family proteins.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
authors.forename: Yongchan
authors.initials: Y
authors.lastname: Lee
authors.affiliation: 1] Department of Biological Sciences, Graduate School of Science, University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan [2] Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Nishizawa
authors.affiliation: RIKEN SPring-8 Center, Hyogo 679-5148, Japan.
authors.forename: Keitaro
authors.initials: K
authors.lastname: Yamashita
authors.affiliation: Department of Biological Sciences, Graduate School of Science, University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
authors.forename: Ryuichiro
authors.initials: R
authors.lastname: Ishitani
authors.affiliation: Department of Biological Sciences, Graduate School of Science, University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Nureki
mesh_terms: D001692:Biological Transport; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship
chemical_list: D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins