title: Structure of a bacterial energy-coupling factor transporter.
abstract: The energy-coupling factor (ECF) transporters constitute a novel family of conserved membrane transporters in prokaryotes that have a similar domain organization to the ATP-binding cassette transporters. Each ECF transporter comprises a pair of cytosolic ATPases (the A and A' components, or EcfA and EcfA'), a membrane-embedded substrate-binding protein (the S component, or EcfS) and a transmembrane energy-coupling component (the T component, or EcfT) that links the EcfA-EcfA' subcomplex to EcfS. The structure and transport mechanism of the quaternary ECF transporter remain largely unknown. Here we report the crystal structure of a nucleotide-free ECF transporter from Lactobacillus brevis at a resolution of 3.5 Å. The T component has a horseshoe-shaped open architecture, with five α-helices as transmembrane segments and two cytoplasmic α-helices as coupling modules connecting to the A and A' components. Strikingly, the S component, thought to be specific for hydroxymethyl pyrimidine, lies horizontally along the lipid membrane and is bound exclusively by the five transmembrane segments and the two cytoplasmic helices of the T component. These structural features suggest a plausible working model for the transport cycle of the ECF transporters.
authors.affiliation: Ministry of Education Key Laboratory of Protein Science, Tsinghua University, Beijing 100084, China.
authors.forename: Tingliang
authors.initials: T
authors.lastname: Wang
authors.forename: Guobin
authors.initials: G
authors.lastname: Fu
authors.forename: Xiaojing
authors.initials: X
authors.lastname: Pan
authors.forename: Jianping
authors.initials: J
authors.lastname: Wu
authors.forename: Xinqi
authors.initials: X
authors.lastname: Gong
authors.forename: Jiawei
authors.initials: J
authors.lastname: Wang
authors.forename: Yigong
authors.initials: Y
authors.lastname: Shi
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism; D052196:Levilactobacillus brevis / Q000737:chemistry*; D008954:Models, Biological; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D011743:Pyrimidines / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D018528:ATP-Binding Cassette Transporters; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D021122:Protein Subunits; D011743:Pyrimidines