title: SecB is a bona fide generalized chaperone in Escherichia coli.
abstract: It is known that the DnaK and Trigger Factor (TF) chaperones cooperate in the folding of newly synthesized cytosolic proteins in Escherichia coli. We recently showed that despite a very narrow temperature range of growth and high levels of aggregated cytosolic proteins, E. coli can tolerate deletion of both chaperones, suggesting that other chaperones might be involved in this process. Here, we show that the secretion-dedicated chaperone SecB efficiently suppresses both the temperature sensitivity and the aggregation-prone phenotypes of a strain lacking both TF and DnaK. SecB suppression is independent of a productive interaction with the SecA subunit of the translocon. Furthermore, in vitro cross-linking experiments demonstrate that SecB can interact both co- and posttranslationally with short nascent chains of both secretory and cytosolic proteins. Finally, we show that such cotranslational substrate recognition by SecB is greatly suppressed in the presence of ribosome-bound TF, but not by DnaK. Taken together, our data demonstrate that SecB acts as a bona fide generalized chaperone.
authors.affiliation: Department of Molecular Microbiology, Vrije Universiteit, 1081 HV, Amsterdam, The Netherlands.
authors.forename: Ronald S
authors.initials: RS
authors.lastname: Ullers
authors.forename: Joen
authors.initials: J
authors.lastname: Luirink
authors.forename: Nellie
authors.initials: N
authors.lastname: Harms
authors.forename: Françoise
authors.initials: F
authors.lastname: Schwager
authors.forename: Costa
authors.initials: C
authors.lastname: Georgopoulos
authors.forename: Pierre
authors.initials: P
authors.lastname: Genevaux
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D004926:Escherichia coli / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism*; D019696:Peptidylprolyl Isomerase / Q000378:metabolism; D017510:Protein Folding
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; C057842:SecB protein, Bacteria; D012321:DNA-Directed RNA Polymerases; C105078:RNA polymerase beta subunit; C063842:dnaK protein, E coli; C403324:trigger factor, E coli; D019696:Peptidylprolyl Isomerase