title: Escherichia coli trigger factor is a prolyl isomerase that associates with nascent polypeptide chains.
abstract: Correct folding of newly synthesized proteins is proposed to be assisted by molecular chaperones and folding catalysts. To identify cellular factors involved in the initial stages of this process we searched for proteins associated with nascent polypeptide chains. In an Escherichia coli transcription/translation system synthesizing beta-galactosidase we identified a 58-kDa protein which associated with translating ribosomes but dissociated from these ribosomes upon release of nascent beta-galactosidase. N-terminal sequencing identified it as trigger factor, previously implicated in protein secretion. Direct evidence for association of trigger factor with nascent polypeptide chains was obtained by crosslinking. In a wheat germ translation system complemented with E. coli lysates, epsilon-4-(3-trifluoromethyldiazirino)benzoic acid-lysine residues were incorporated into nascent secretory preprolactin and a nonsecretory preprolactin mutant. Trigger factor crosslinked to both types of nascent chains, provided they were ribosome bound. Trigger factor contains key residues of the substrate-binding pocket of FK506-binding protein-type peptidyl-prolyl-cis/trans-isomerases and has prolyl isomerase activity in vitro. We propose that trigger factor is a folding catalyst acting cotranslationally.
authors.affiliation: Zentrum für Molekulare Biologie, Universität Heidelberg, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Hesterkamp
authors.forename: S
authors.initials: S
authors.lastname: Hauser
authors.forename: H
authors.initials: H
authors.lastname: Lütcke
authors.forename: B
authors.initials: B
authors.lastname: Bukau
mesh_terms: D000591:Amino Acid Isomerases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000737:chemistry; D002352:Carrier Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D018833:Chaperonins / Q000378:metabolism*; D003432:Cross-Linking Reagents; D004268:DNA-Binding Proteins / Q000737:chemistry; D004926:Escherichia coli / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D016296:Mutagenesis; D019696:Peptidylprolyl Isomerase; D011388:Prolactin / Q000096:biosynthesis; D014176:Protein Biosynthesis; D017510:Protein Folding; D011498:Protein Precursors / Q000096:biosynthesis; D011691:Puromycin / Q000494:pharmacology; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D022021:Tacrolimus Binding Proteins; D014158:Transcription, Genetic; D014908:Triticum; D001616:beta-Galactosidase / Q000096:biosynthesis
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D003432:Cross-Linking Reagents; D004268:DNA-Binding Proteins; D006360:Heat-Shock Proteins; D011498:Protein Precursors; D011691:Puromycin; C017671:preprolactin; D011388:Prolactin; D001616:beta-Galactosidase; D018833:Chaperonins; D000591:Amino Acid Isomerases; D022021:Tacrolimus Binding Proteins; D019696:Peptidylprolyl Isomerase