title: The long alpha-helix of SecA is important for the ATPase coupling of translocation.
abstract: SecA contains two ATPase folds (NBF1 and NBF2) and other interaction/regulatory domains, all of which are connected by a long helical scaffold domain (HSD) running along the molecule. Here we identified a functionally important and spatially adjacent pair of SecA residues, Arg-642 on HSD and Glu-400 on NBF1. A charge-reversing substitution at either position as well as disulfide tethering of these positions inactivated the translocation activity. Interestingly, however, the translocation-inactive SecA variants fully retained the ability to up-regulate the ATPase in response to a preprotein and the SecYEG translocon. The translocation defect was suppressible by second site alterations at the hinge-forming boundary of NBF2 and HSD. Based on these results, we propose that the motor function of SecA is realized by ligand-activated ATPase engine and its HSD-mediated conversion into the mechanical work of preprotein translocation.
authors.affiliation: Institute for Virus Research, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Mori
authors.forename: Koreaki
authors.initials: K
authors.lastname: Ito
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000502:physiology; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000502:physiology*; D001665:Binding Sites; D003545:Cysteine / Q000737:chemistry; D004926:Escherichia coli / Q000378:metabolism; D005816:Genetic Complementation Test; D008024:Ligands; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000502:physiology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D021381:Protein Transport; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
chemical_list: D001426:Bacterial Proteins; D008024:Ligands; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins; D003545:Cysteine