title: Three-dimensional structure of the sugar symporter melibiose permease from cryo-electron microscopy.
abstract: Melibiose permease (MelB) of Escherichia coli is a secondary transporter that couples the uptake of melibiose and various other galactosides to symport of cations that can be Na+, Li+ or H+. MelB belongs to the glycoside-pentoside-hexuronide: cation symporter family of porters and is suggested to have 12 transmembrane helices. We have determined the three-dimensional structure of MelB at 10A resolution in the membrane plane with cryo-electron microscopy from two-dimensional crystals. The three-dimensional map shows a heart-shaped molecule composed of two domains with a large central cavity between them. The structure is constricted at one side of the membrane while it is open to the other. The overall molecular shape resembles those of lactose permease and glycerol-3-phosphate transporter. However, organization of helices in MelB seems less symmetrical than in these two members of the major facilitator superfamily.
authors.affiliation: Karolinska Institutet, Department of Biosciences at Novum, S-141 57 Huddinge,Sweden.
authors.forename: Pasi
authors.initials: P
authors.lastname: Purhonen
authors.forename: Anna-Karin
authors.initials: AK
authors.lastname: Lundbäck
authors.forename: Raymonde
authors.initials: R
authors.lastname: Lemonnier
authors.forename: Gérard
authors.initials: G
authors.lastname: Leblanc
authors.forename: Hans
authors.initials: H
authors.lastname: Hebert
mesh_terms: D020285:Cryoelectron Microscopy; D003461:Crystallography; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000648:ultrastructure; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D027981:Symporters / Q000737:chemistry* / Q000648:ultrastructure
chemical_list: D029968:Escherichia coli Proteins; D027981:Symporters; C021548:melibiose permease