title: Solution NMR structure and X-ray absorption analysis of the C-terminal zinc-binding domain of the SecA ATPase.
abstract: The solution NMR structure of a 22-residue Zn(2+)-binding domain (ZBD) from Esherichia coli preprotein translocase subunit SecA is presented. In conjunction with X-ray absorption analysis, the NMR structure shows that three cysteines and a histidine in the sequence CXCXSGX(8)CH assume a tetrahedral arrangement around the Zn(2+) atom, with an average Zn(2+)-S bond distance of 2.30 A and a Zn(2+)-N bond distance of 2.03 A. The NMR structure shows that ND1 of His20 binds to the Zn(2+) atom. The ND1-Zn(2+) bond is somewhat strained: it makes an angle of approximately 17 degrees with the plane of the ring, and it also shows a significant "in-plane" distortion of 13 degrees. A comprehensive sequence alignment of the SecA-ZBD from many different organisms shows that, along with the four Zn(2+) ligands, there is a serine residue (Ser12) that is completely conserved. The NMR structure indicates that the side chain of this serine residue forms a strong hydrogen bond with the thiolate of the third cysteine residue (Cys19); therefore, the conserved serine appears to have a critical role in the structure. SecB, an export-specific chaperone, is the only known binding partner for the SecA-ZBD. A phylogenetic analysis using 86 microbial genomes shows that 59 of the organisms carry SecA with a ZBD, but only 31 of these organisms also possess a gene for SecB, indicating that there may be uncharacterized binding partners for the SecA-ZBD.
authors.affiliation: Department of Biochemistry, University of Western Ontario, London ON N6A 5C1, Ontario, Canada.
authors.forename: Brian R
authors.initials: BR
authors.lastname: Dempsey
authors.forename: Mark
authors.initials: M
authors.lastname: Wrona
authors.forename: Jana M
authors.initials: JM
authors.lastname: Moulin
authors.forename: Gregory B
authors.initials: GB
authors.lastname: Gloor
authors.forename: Farideh
authors.initials: F
authors.lastname: Jalilehvand
authors.forename: Gilles
authors.initials: G
authors.lastname: Lajoie
authors.forename: Gary S
authors.initials: GS
authors.lastname: Shaw
authors.forename: Brian H
authors.initials: BH
authors.lastname: Shilton
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D004577:Electron Probe Microanalysis; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010802:Phylogeny; D011487:Protein Conformation; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D017386:Sequence Homology, Amino Acid; D015032:Zinc / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins; D015032:Zinc