Inhibitor-Induced Structural Changes in Serine Proteases Monitored by Fourier Transform Infrared Spectroscopy

Abstract

Serine proteases are an important family of enzymes whose members participate in a variety of biological activities such as digestion and coagulation.The three-dimensional structure of some of the digestive serine proteases, its inhibitors and their complexes have been determined to a very high atomic resolution.In this paper, conformational perturbations in enzymes (trypsin subfamily) caused by binding of synthetic and natural inhibitors and solvent changes are examined. The changes are monitored by comparison of second-derivative FTIR spectra of inhibited and uninhibited enzymes in solution (H 2 O).The results are compared to those obtained from X-ray crystallography studies.Infrared absorption spectroscopy was first introduced as a tool for the study of peptide and protein conformations more than 40 years ago (1). In the IR absorption spectrum, amide groups are strong chromophores that give rise to nine strong characteristic bands, named amide A, Β and I-VII. Among these bands, amide I band (which is due mostly to the C=0 stretching vibrations of the peptide backbone) has been primarily used for protein secondary structure determination studies due to its high sensitivity to small changes in molecular geometry and hydrogen bonding of the peptide group.It was recognized early on that for proteins in solution, amide I band is broad and featureless and for proteins that contain segments with different conformations, the results are not always easy to interpret 0097-6156/94/0576-0235$08.00/0