title: Substrate specificity of the SecB chaperone.
abstract: The bacterial chaperone SecB assists translocation of proteins across the inner membrane. The mechanism by which it differentiates between secretory and cytosolic proteins is poorly understood. To identify its binding motif, we screened 2688 peptides covering sequences of 23 proteins for SecB binding. The motif is approximately 9 residues long and is enriched in aromatic and basic residues, whereas acidic residues are disfavored. Its identification allows the prediction of binding regions within protein sequences with up to 87% accuracy. SecB-binding regions occur statistically every 20-30 residues. The occurrence and affinity of binding regions are similar in SecB-dependent and -independent secretory proteins and in cytosolic proteins, and SecB lacks specificity toward signal sequences. SecB cannot thus differentiate between secretory and non-secretory proteins via its binding specificity. This conclusion is supported by the finding that SecB binds denatured luciferase, thereby allowing subsequent refolding by the DnaK system. SecB may rather be a general chaperone whose involvement in translocation is mediated by interactions of SecB and signal sequences of SecB-bound preproteins with the translocation apparatus.
authors.affiliation: Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany.
authors.forename: N T
authors.initials: NT
authors.lastname: Knoblauch
authors.forename: S
authors.initials: S
authors.lastname: Rüdiger
authors.forename: H J
authors.initials: HJ
authors.lastname: Schönfeld
authors.forename: A J
authors.initials: AJ
authors.lastname: Driessen
authors.forename: J
authors.initials: J
authors.lastname: Schneider-Mergener
authors.forename: B
authors.initials: B
authors.lastname: Bukau
mesh_terms: D000596:Amino Acids / Q000032:analysis; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D008156:Luciferases / Q000737:chemistry; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism; D019151:Peptide Library; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D017510:Protein Folding; D021382:Protein Sorting Signals / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012680:Sensitivity and Specificity
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D018832:Molecular Chaperones; D019151:Peptide Library; D010455:Peptides; D021382:Protein Sorting Signals; C057842:SecB protein, Bacteria; D008156:Luciferases; C063842:dnaK protein, E coli