title: Characterization of three areas of interactions stabilizing complexes between SecA and SecB, two proteins involved in protein export.
abstract: The general secretory, Sec, system translocates precursor polypeptides from the cytosol across the cytoplasmic membrane in Escherichia coli. SecB, a small cytosolic chaperone, captures the precursor polypeptides before they fold and delivers them to the membrane translocon through interactions with SecA. Both SecB and SecA display twofold symmetry and yet the complex between the two is stabilized by contacts that are distributed asymmetrically. Two distinct regions of interaction have been defined previously and here we identify a third. Calorimetric studies of complexes stabilized by different subsets of these interactions were carried out to determine the binding affinities and the thermodynamic parameters that underlie them. We show here that there is no change in affinity when either one of two contact areas out of the three is lacking. This fact and the asymmetry of the binding contacts may be important to the function of the complex in protein export.
authors.affiliation: Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, USA.
authors.forename: Chetan N
authors.initials: CN
authors.lastname: Patel
authors.forename: Virginia F
authors.initials: VF
authors.lastname: Smith
authors.forename: Linda L
authors.initials: LL
authors.lastname: Randall
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002151:Calorimetry / Q000379:methods; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D046912:Multiprotein Complexes; D009154:Mutation; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D046912:Multiprotein Complexes; D000069816:SEC Translocation Channels; C057842:SecB protein, Bacteria; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins