A conformational isomer of bovine pancreatic trypsin inhibitor protein produced by refolding.

Abstract

Refolding of the bovine pancreatic trypsin inhibitor protein (BPTI) after reduction of its three cysteine disulphide linkages can occur when the reduced protein is placed in a suitable oxidizing medium (ref. 1 and refs therein). The refolding process has been studied by trapping chemically intermediates which contain only one or two disulphide bonds (ref. 1 and refs therein). We report here that during structural studies of these intermediates by NMR, we have found that complete re-oxidation of the protein results in substantial quantities of a metastable folded species which is identical to native BPTI in its covalent bonding (including the disulphide bonds) but possesses a somewhat different conformation. The existence of such a species is supported by circular dichroism measurements on refolded BPTI. This novel form of BPTI is of considerable interest because it can be used to provide information about the folding mechanism and conformational stability of the protein.