Reaction-induced FT-IR spectroscopic studies of biological energy conversion in oxygenic photosynthesis and transport

While membrane-associated proteins make up a substantial percentage of tota l cellular proteins, a much smaller fraction of known X-ray and NMR protein structures are derived from membrane proteins, Alternative approaches to u nderstanding structure, function, and mechanism in membrane-associated enzy mes are clearly needed. Vibrational FT-IR spectroscopy offers a method by w hich high-resolution structural and dynamic information can be obtained abo ut this class of proteins. Reaction-induced FT-IR spectroscopy is an implem entation of vibrational spectroscopy, in which the difference spectrum asso ciated with a perturbative stimulus is recorded. This approach simplifies t he spectrum and monitors the structural changes directly involved in the fu nctional transition. In this article, we describe reaction-induced FT-IR st udies of the photosynthetic and transport proteins, photosystem II, photosy stem I, and lactose permease. In oxygenic plant photosynthesis, photosystem II and I convert Light energy to chemical energy. In secondary active tran sport, the permease converts an electrochemical gradient into the energy re quired to move lactose into the cell. Reaction-induced FT-IR spectra acquir ed from these proteins can identify intermediates in the reaction mechanism . Vibrational bands in spectra acquired from photosystem II, photosystem I, and the permease are assigned by a combination of site-directed mutagenesi s, isotopic labeling, and kinetic techniques. This article summarizes our r ecent progress in the study of photosynthetic and transport proteins with r eaction-induced PT-IR spectroscopy.