PARTIALLY FOLDED, MOLTEN GLOBULE AND MOLTEN COIL STATES OF BOVINE PANCREATIC TRYPSIN-INHIBITOR

Three denatured states of bovine pancreatic trypsin inhibitor have been characterized, using two chemically synthesized analogues designed for study of folding intermediates. One analogue, [14-38](Abu), retains only the 14-38 disulphide. At ph 4.5-6 and 1-7 degrees C, [14-38](Abu) is a highly ordered beta-sheet molten globule; it has the circular dichroism (CD), ANS-binding and folding kinetics of a molten globule; is partially folded by NMR analysis; and undergoes cooperative thermal denaturation. At low temperature [14-38](Abu) also forms an acid state at pH 1.5, as well as a denatured state at ph 2.5. A second BPTI analogue with all three disulphide bridges eliminated, [R](Abu), lacks detectable secondary and tertiary structure but has stable hydrophobic surfaces and is collapsed, We term this species a 'molten coil'.