OCCURRENCE OF TRANSIENT MULTIMERIC SPECIES DURING THE REFOLDING OF A MONOMERIC PROTEIN

A set of protein fragments from yeast phosphoglycerate kinase were pro duced by chemical cleavage at a unique cysteinyl residue previously in troduced by site-directed mutagenesis. Cross-linking experiments showe d that the fragments corresponding to incomplete N-terminal domain for m stable oligomeric species. Transient oligomeric species were also ob served by both cross-linking and light scattering experiments during t he folding process of the whole protein. These transient oligomeric sp ecies are formed during the fast folding phase and dissociate during t he slow folding phase to produce the monomeric active protein. The mul timeric species are not required for the protein to fold correctly. Un expectedly, the distribution of oligomeric species is not dependent on protein concentration during the folding process. A kinetic competiti on mechanism is proposed as a possible solution to this paradox. These results provide direct evidence that the polypeptide chain can explor e nonnative interactions during the folding process.