The c-terminal (331-376) sequence of Escherichia coli DnaJ is essential for dimerization and chaperone activity -: A small angle x-ray scattering study in solution

DnaJ, an Escherichia coli Hsp40 protein composed of 376 amino acid residues, is a chaperone with thioldisulfide oxidoreductase activity. We present here for the first time a small angle x-ray scattering study of intact DnaJ and a truncated version, DnaJ (1-330), in solution. The molecular weight of DnaJ and DnaJ (1-330) determined by both small angle x-ray scattering and size-exclusion chromatography provide direct evidence that DnaJ is a homodimer and DnaJ (1-330) is a monomer. The restored models show that DnaJ is a distorted omega-shaped dimeric molecule with the C terminus of each subunit forming the central part of the omega, whereas DnaJ (1-330) exists as a monomer. This indicates that the deletion of the C-terminal 46 residues of DnaJ impairs the association sites, although it does not cause significant conformational changes. Biochemical studies reveal that DnaJ (1-330), while fully retaining its thiol-disulfide oxidoreductase activity, is structurally less stable, and its peptide binding capacity is severely impaired relative to that of the intact molecule. Together, our results reveal that the C-terminal (331-376) residues are directly involved in dimerization, and the dimeric structure of DnaJ is necessary for its chaperone activity but not required for the thiol-disulfide oxidoreductase activity.