DEPENDENCE OF THE ANTI-CHAPERONE ACTIVITY OF PROTEIN DISULFIDE-ISOMERASE ON ITS CHAPERONE ACTIVITY

Protein disulphide isomerase (PDI) shows chaperone and anti-chaperone activities in assisting refolding of denatured and reduced lysozyme in redox Hepes buffer, but only chaperone activity in phosphate buffer a nd redox Hepes buffer containing 0.1 M NaCl. In non-redox Hepes buffer its anti-chaperone activity is very weak. PDI displays its anti-chape rone activity only for those substrates showing relatively low aggrega tion during refolding, and is strongly dependent on refolding conditio ns, of which ionic strength appears to be an important factor. The S-m ethylated PDI, fully active as a chaperone but devoid of isomerase act ivity, by itself shows only anti-chaperone activity, but reinforces ra ther than suppresses the chaperone activity of native PDI in the refol ding of lysozyme. A fragment of PDI with the C-terminal peptide-bindin g sequence removed and devoid of chaperone activity does not show anti -chaperone activity in lysozyme refolding. It appears that the anti-ch aperone activity of PDI is dependent on its chaperone activity.