Independent refolding of domains in the pancreatic serine proteinases

Ser-neotrypsinogen and Val-neotrypsinogen are two-chain modifications of bovine trypsinogen produced on limited proteolysis with trypsin. Ser-neotrypsinogen has Lys131-Ser132 cleaved in the connecting peptide (the autolysis loop) linking the amino- and carboxyl-terminal domains. Val-neotrypsinogen has Arg105-Val106 cleaved which is located within the amino-terminal domain. The mixed disulfide derivative of Ser-neotrypsinogen was successfully refolded. A functional molecule was regenerated from the polypeptide fragments with the correct molecular weight of neotrypsinogen in an overall yield of 7%. Val-Neotrypsinogen could not be refolded. The first-order rate constants for the regeneration of Ser-neotrypsinogen were determined from the formation of active enzyme molecules as a function of time and from the regain of the correct molecular weight. Both kinetic values were the same indicating that refolding of the polypeptide chains first forms globular domain structures. The two domains then associate and the disulfide bonds between the domains and the correct geometry of the active site residues are formed last. The same kinetic results were also found in refolding Thr-neochymotrypsinogen (Duda, C. T., and Light, A. (1982) J. Biol. Chem. 257, 9866-9871) where peptide bond cleavage also occurred in the connecting peptide. These observations support the hypothesis that the pathway of folding of serine proteinases proceeds with the independent refolding of domains.