Fourier Transform Infrared Spectroscopy of Calcium-Binding Proteins

Abstract

Infrared spectroscopy measures absorptions of vibrating molecules and yields information about molecular structure and structural interactions. Over the last two decades, the infrared technique has emerged as a very useful tool for examining protein conformation as a result of the increase in energy throughput, achievable signal-to-noise ratio, wavenumber accuracy, and data aquisition rates that came with the development of Fourier transform infrared (FTIR) spectrometers. High-quality infrared spectra can now rapidly be aquired and require only relatively small amounts of protein. The size of the protein or the nature of the environment does not limit the application of FTIR spectroscopy. Importantly, measurements of proteins in aqueous solution are almost routine now. Furthermore, the process of obtaining structural information is not restricted to a static picture, but can also be achieved in real time by applying time-resolved infrared techniques. The effects of environmental factors, point mutations, or ligand binding on the structure of the proteins can be examined with high sensitivity by using peptide backbone and side-chain infrared bands as conformation-sensitive monitors. In combination with isotope labeling, the technique also permits the study of protein-protein or protein-peptide interactions.