title: Complex behavior in solution of homodimeric SecA.
abstract: SecA, a homodimeric protein involved in protein export in Escherichia coli, exists in the cell both associated with the membrane translocation apparatus and free in the cytosol. SecA is a multifunctional protein involved in protein localization and regulation of its own expression. To carry out these functions, SecA interacts with a variety of proteins, phospholipids, nucleotides, and nucleic acid and shows two enzymic activities. It is an ATPase and a helicase. Its role during protein localization involves interaction with the precursor polypeptides to be exported, the cytosolic chaperone SecB, and the SecY subunit of the membrane-associated translocase, as well as with acidic phospholipids. At the membrane, SecA undergoes a cycle of binding and hydrolysis of ATP coupled to conformational changes that result in translocation of precursors through the cytoplasmic membrane. The helicase activity of SecA and its affinity for its mRNA are involved in regulation of its own expression. SecA has been reported to exist in at least two conformational states during its functional cycle. Here we have used analytical centrifugation, as well as column chromatography coupled with multi-angle light scatter, to show that in solution SecA undergoes at least two monomer-dimer equilibrium reactions that are sensitive to temperature and to concentration of salt.
authors.affiliation: School of Molecular Biosciences, Washington State University, Pullman, Washington 99164-4660, USA.
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Woodbury
authors.forename: Simon J S
authors.initials: SJ
authors.lastname: Hardy
authors.forename: Linda L
authors.initials: LL
authors.lastname: Randall
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism / Q000502:physiology*; D001419:Bacteria / Q000378:metabolism*; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D008027:Light; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D008970:Molecular Weight; D011485:Protein Binding; D011498:Protein Precursors / Q000378:metabolism*; D000069816:SEC Translocation Channels; D012542:Scattering, Radiation; D000081416:SecA Proteins; D012996:Solutions; D014461:Ultracentrifugation
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011498:Protein Precursors; D000069816:SEC Translocation Channels; D012996:Solutions; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins