Secondary structure formation is the earliest structural event in the refolding of an all beta-sheet protein

The refolding kinetics of cobrotoxin (CBTX), a small-molecular-weight (simi lar to 7 kDa) all beta-sheet protein, has been monitored using a variety of biophysical techniques. The secondary structure formation and hydrophobic collapse occur as distinct events during the refolding of the protein. Comp lete secondary structure formation occurs prior to the clustering of the hy drophobic residues. The late stage(s) of the refolding pathway of CBTX is c haracterized by change(s) in the local environment and optical asymmetry of the indole ring of the sole tryptophan residue. The results obtained in th e present study, to our knowledge, represent the first unambiguous experime ntal support for the framework model of protein folding. (C) 1999 Academic Press.