PRESSURE-INDUCED STRUCTURAL REARRANGEMENTS OF BOVINE PANCREATIC TRYPSIN-INHIBITOR STUDIED BY FTIR SPECTROSCOPY

Fourier transform infrared (FTIR) spectroscopy combined with resolutio n enhancement techniques, second-derivative and difference spectroscop ies, have been used to characterize pressure-induced changes in the st ructural rearrangements of bovine pancreatic trypsin inhibitor (BPTI) in D2O solution at 25.0 degrees C. According to the observed changes i n the amide I' band up to 550 MPa, the secondary structure elements of BPTI, such as the alpha-helix, 3(10)-helix, beta-sheet, and beta-turn , are scarcely rearranged except for the loop structure of residues of 9-17 and 36-43. The polypeptide backbone is not extensively unfolded up to 550 MPa. The minor pressure-induced structural rearrangements ar e completely reversible. A further increase in pressure above 1000 MPa associated with the precipitation of BPTI in D2O buffer solution indu ces the partial structural rearrangements of the alpha-helix, beta-tur n and/or 3(10)-helix, and beta-sheet. The polypeptide backbone of BPTI is not fully unfolded even above 1000 MPa. Most of the protected back bone amide protons involved in the beta-sheet remain intact in the pre ssure range where BPTI is not precipitated, while those involved in th e alpha-helix and beta-turn and/or 3(10)-helix are exchanged with solv ent deuterons. The protected backbone amide protons located near the s urface regions are more easily exchanged with solvent deuterons by app lication of high pressure than those involved in the core. (C) 1998 Jo hn Wiley & Sons, Inc.