Trigger Factor and DnaK possess overlapping substrate pools and binding specificities.
Ribosome-associated Trigger Factor (TF) and the DnaK chaperone system assist the folding of newly synthesized proteins in Escherichia coli. Here, we show that DnaK and TF share a common substrate pool in vivo. In TF-deficient cells, deltatig, depleted for DnaK and DnaJ the amount of aggregated proteins increases with increasing temperature, amounting to 10% of total soluble protein (approximately 340 protein species) at 37 degrees C. A similar population of proteins aggregated in DnaK depleted tig+ cells, albeit to a much lower extent. Ninety-four aggregated proteins isolated from DnaK- and DnaJ-depleted deltatig cells were identified by mass spectrometry and found to include essential cytosolic proteins. Four potential in vivo substrates were screened for chaperone binding sites using peptide libraries. Although TF and DnaK recognize different binding motifs, 77% of TF binding peptides also associated with DnaK. In the case of the nascent polypeptides TF and DnaK competed for binding, however, with competitive advantage for TF. In vivo, the loss of TF is compensated by the induction of the heat shock response and thus enhanced levels of DnaK. In summary, our results demonstrate that the co-operation of the two mechanistically distinct chaperones in protein folding is based on their overlap in substrate specificities.
Deuerling
Elke
E
Zentrum für Molekulare Biologie (ZMBH), Universität Heidelberg, INF282, D-69120 Heidelberg, Germany. e.deuer ling@zmbh.uni-heidelberg.de
Patzelt
Holger
H
Vorderwülbecke
Sonja
S
Rauch
Thomas
T
Kramer
Günter
G
Schaffitzel
Elke
E
Mogk
Axel
A
Schulze-Specking
Agnes
A
Langen
Hanno
H
Bukau
Bernd
B
D018834:Chaperonin 60 / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism*; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism; D019696:Peptidylprolyl Isomerase / Q000378:metabolism*; D011485:Protein Binding; D017510:Protein Folding; D025941:Protein Interaction Mapping; D013379:Substrate Specificity
D018834:Chaperonin 60; C494635:DnaJ protein, E coli; D029968:Escherichia coli Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C063842:dnaK protein, E coli; C403324:trigger factor, E coli; D019696:Peptidylprolyl Isomerase