title: L23 protein functions as a chaperone docking site on the ribosome.
abstract: During translation, the first encounter of nascent polypeptides is with the ribosome-associated chaperones that assist the folding process--a principle that seems to be conserved in evolution. In Escherichia coli, the ribosome-bound Trigger Factor chaperones the folding of cytosolic proteins by interacting with nascent polypeptides. Here we identify a ribosome-binding motif in the amino-terminal domain of Trigger Factor. We also show the formation of crosslinked products between Trigger Factor and two adjacent ribosomal proteins, L23 and L29, which are located at the exit of the peptide tunnel in the ribosome. L23 is essential for the growth of E. coli and the association of Trigger Factor with the ribosome, whereas L29 is dispensable in both processes. Mutation of an exposed glutamate in L23 prevents Trigger Factor from interacting with ribosomes and nascent chains, and causes protein aggregation and conditional lethality in cells that lack the protein repair function of the DnaK chaperone. Purified L23 also interacts specifically with Trigger Factor in vitro. We conclude that essential L23 provides a chaperone docking site on ribosomes that directly links protein biosynthesis with chaperone-assisted protein folding.
authors.affiliation: Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, 79104 Freiburg, Germany.
authors.forename: Günter
authors.initials: G
authors.lastname: Kramer
authors.forename: Thomas
authors.initials: T
authors.lastname: Rauch
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Rist
authors.forename: Sonja
authors.initials: S
authors.lastname: Vorderwülbecke
authors.forename: Holger
authors.initials: H
authors.lastname: Patzelt
authors.forename: Agnes
authors.initials: A
authors.lastname: Schulze-Specking
authors.forename: Nenad
authors.initials: N
authors.lastname: Ban
authors.forename: Elke
authors.initials: E
authors.lastname: Deuerling
authors.forename: Bernd
authors.initials: B
authors.lastname: Bukau
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D003432:Cross-Linking Reagents; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013058:Mass Spectrometry; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D019696:Peptidylprolyl Isomerase / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012269:Ribosomal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D003432:Cross-Linking Reagents; D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; D012269:Ribosomal Proteins; C043816:ribosomal protein L23, E coli; C035078:ribosomal protein L29; C403324:trigger factor, E coli; D019696:Peptidylprolyl Isomerase