Attenuated total reflection IR spectroscopy as a tool to investigate the structure, orientation and tertiary structure changes in peptides and membrane proteins

During the last few years, attenuated total reflection Fourier transform in frared spectroscopy (ATR-FTIR) has become one of the most powerful methods to determine the structure of biological materials and in particular of com ponents of biological membranes, like proteins that cannot be studied by x- ray crystallography and NMR. ATR-FTIR requires a little amount of material (1-100 mug) and spectra are recorded in a matter of minutes. The environmen t of the molecules can be modulated so that their conformation can be studi ed as a function of temperature, pressure, pH, as well as in the presence o f specific ligands. For instance, replacement of amide hydrogen by deuteriu m is extremely sensitive to environmental changes and the kinetics of excha nge can be used to detect tertiary conformational changes in the protein st ructure. Moreover, in addition to the conformational parameters that can be deduced from the shape of the infrared spectra, the orientation of various parts of the molecule can be estimated with polarized IR. This allows more precise analysis of the general architecture of the membrane molecules wit hin the biological membranes. The present review focuses on ATR-IR as an ex perimental approach of special interest for the study of the structure, ori entation, and tertiary structure changes lit peptides and membrane proteins . (C) 2001 John Wiley & Sons, Inc.