Abstract
The DnaK chaperone system, consisting of DnaK, DnaJ, and GrpE, remodels and refolds proteins during both normal growth and stress conditions. CbpA, one of several DnaJ analogs in Escherichia coli, is known to function as a multicopy suppressor for dnaJ mutations and to bind nonspecifically to DNA and preferentially to curved DNA. We found that CbpA functions as a DnaJ-like co-chaperone in vitro. CbpA acted in an ATP-dependent reaction with DnaK and GrpE to remodel inactive dimers of plasmid P1 RepA into monomers active in P1 DNA binding. Additionally, CbpA participated with DnaK in an ATP-dependent reaction to prevent aggregation of denatured rhodanese. The cbpA gene is in an operon with an open reading frame, yccD, which encodes a protein that has some homology to DafA of Thermus thermophilus. DafA is a protein required for the assembly of ring-like particles that contain trimers each of T. thermophilus DnaK, DnaJ, and DafA. The E. coli YccD was isolated because of its potential functional relationship to CbpA. Purified YccD specifically inhibited both the co-chaperone activity and the DNA binding activity of CbpA, suggesting that YccD modulates the activity of CbpA. We named the product of the yccD gene CbpM for "CbpA modulator."
Highlights
The current model for the mechanism of reactivation of heatinactivated proteins by DnaK is that ATP-bound DnaK binds and releases heat-denatured polypeptides rapidly through in
We suggested a model for the mechanism of native protein remodeling by the DnaK chaperone system in which native substrates are bound by DnaJ through exposed high affinity DnaJ binding sites [8]
A cbpA deletion mutant exhibits no apparent growth phenotypes; a cbpA,dnaJ double deletion strain is unable to grow below 16 °C or above 37 °C, a phenotype resembling that of dnaK deletion strains [14]
Summary
Vol 279, No 32, Issue of August 6, pp. 33147–33153, 2004 Printed in U.S.A. CbpA, a DnaJ Homolog, Is a DnaK Co-chaperone, and Its Activity Is Modulated by CbpM*ࡗ. We suggested a model for the mechanism of native protein remodeling by the DnaK chaperone system in which native substrates are bound by DnaJ through exposed high affinity DnaJ binding sites [8]. The protein encoded by yccD, which shares some homology to DafA of Thermus thermophilus, was isolated and found to interact with CbpA. The consequence of this interaction was the inhibition of both the DnaJ-like co-chaperone activity and the DNA binding activity of CbpA. Based on these results, the product of the yccD gene has been named CbpM, for “CbpA modulator.”. The product of the yccD gene has been named CbpM, for “CbpA modulator.” Together CbpA and CbpM are capable of activating and modulating the activity of the DnaK chaperone system, respectively
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