title: Evaluation of similarities in the cis/trans isomerase function of trigger factor and DnaK.
abstract: Two functionally redundant enzymes, trigger factor and the hsp70 chaperone DnaK, have been found to assist de novo protein folding in E coli. Trigger factor is a peripheral peptidyl prolyl cis/trans isomerase (PPIase) of the large subunit of the ribosome. In contrast, DnaK displays two catalytic features: the secondary amide peptide bond cis/trans isomerase (APIase) function supplemented by the ATPase site. APIases accelerate the cis/trans isomerization of nonprolyl peptide bonds. Both enzymes have affinity for an unfolded polypeptide chain. The diminished low temperature cell viability in the presence of trigger factor variants with impaired PPlase activity indicates that the enhancement of folding rates plays a crucial role in protein folding in vivo. For the DnaK-mediated increase in the folding yield in vitro, the minimal model for APlase catalysis involves the catalyzed partitioning of a rapidly formed folding intermediate as could be inferred from the DnaK/DnaJ/GrpE/ATP-assisted refolding of GdmCl-denatured luciferase. Using three different peptide bond cis/trans isomerization assays in vitro, we could show that there is no overlapping substrate specificity of trigger factor and DnaK. We propose that only if trigger factor recruits supplementing molecules is it capable of exhibiting functional complementarity with DnaK in protein folding.
authors.affiliation: Max Planck Research Unit for Enzymology of Protein Folding, Weinbergweg 22, D-06120 Halle/Saale, Germany.
authors.forename: Cordelia
authors.initials: C
authors.lastname: Schiene-Fischer
authors.forename: Judith
authors.initials: J
authors.lastname: Habazettl
authors.forename: Thomas
authors.initials: T
authors.lastname: Tradler
authors.forename: Gunter
authors.initials: G
authors.lastname: Fischer
mesh_terms: D002384:Catalysis; D003001:Cloning, Molecular; D004789:Enzyme Activation / Q000502:physiology; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D007535:Isomerases / Q000235:genetics / Q000378:metabolism*; D008156:Luciferases / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D009154:Mutation / Q000235:genetics; D019696:Peptidylprolyl Isomerase / Q000235:genetics / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics; D017510:Protein Folding; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D011994:Recombinant Proteins; D008156:Luciferases; C063842:dnaK protein, E coli; D007535:Isomerases; C403324:trigger factor, E coli; D019696:Peptidylprolyl Isomerase