Functional analysis of CbpA, a DnaJ homolog and nucleoid-associated DNA-binding protein

DnaK/Hsp70 proteins are universally conserved ATP-dependent molecular chaperones that help proteins adopt and maintain their native conformations. DnaJ/Hsp40 and GrpE are co-chaperones that assist DnaK. CbpA is an Escherichia coli DnaJ homolog. It acts as a multicopy suppressor for dnaJ mutations and functions in vitro in combination with DnaK and GrpE in protein remodeling reactions. CbpA binds nonspecifically to DNA with preference for curved DNA and is a nucleoid-associated protein. The DNA binding and co-chaperone activities of CbpA are modulated by CbpM, a small protein that binds specifically to CbpA. To identify the regions of CbpA involved in the interaction of CbpA with CbpM and those involved in DNA binding, we constructed and characterized deletion and substitution mutants of CbpA. We discovered that CbpA interacted with CbpM through its N-terminal J-domain. We found that the region C-terminal to the J-domain was required for DNA binding. Moreover, we found that the CbpM interaction, DNA binding, and co-chaperone activities were separable; some mutants were proficient in some functions and defective in others.