title: Escherichia coli SecA helicase activity is not required in vivo for efficient protein translocation or autogenous regulation.
abstract: SecA is an essential ATP-driven motor protein that binds to preproteins and the translocon to promote protein translocation across the eubacterial plasma membrane. Escherichia coli SecA contains seven conserved motifs characteristic of superfamily II of DNA and RNA helicases, and it has been shown previously to possess RNA helicase activity. SecA has also been shown to be an autogenous repressor that binds to its translation initiation region on secM-secA mRNA, thereby blocking and dissociating 30 S ribosomal subunits. Here we show that SecA is an ATP-dependent helicase that unwinds a mimic of the repressor helix of secM-secA mRNA. Mutational analysis of the seven conserved helicase motifs in SecA allowed us to identify mutants that uncouple SecA-dependent protein translocation activity from its helicase activity. Helicase-defective secA mutants displayed normal protein translocation activity and autogenous repression of secA in vivo. Our studies indicate that SecA helicase activity is nonessential and does not appear to be necessary for efficient protein secretion and secA autoregulation.
authors.affiliation: Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459, USA.
authors.forename: M O
authors.initials: MO
authors.lastname: Schmidt
authors.forename: R M
authors.initials: RM
authors.lastname: Brosh
authors.forename: D B
authors.initials: DB
authors.lastname: Oliver
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018988:Bacterial Translocation / Q000502:physiology; D017124:Conserved Sequence; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000737:chemistry; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins; D006706:Homeostasis; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D021381:Protein Transport; D012329:RNA, Bacterial / Q000378:metabolism; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D012329:RNA, Bacterial; D000069816:SEC Translocation Channels; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D004265:DNA Helicases; D000081416:SecA Proteins