Structure and dynamics of membrane proteins as studied by infrared spectroscopy

Infrared (IR) spectroscopy is a useful technique in the study of protein co nformation and dynamics. The possibilities of the technique become apparent specially when applied to large proteins in turbid suspensions, as is ofte n the case with membrane proteins. The present review describes the applica tions of IR spectroscopy to the study of membrane proteins, with an emphasi s on recent work and on spectra recorded in the transmission mode, rather t han using reflectance techniques. Data treatment procedures are discussed, including band analysis and difference spectroscopy methods. A technique fo r the analysis of protein secondary and tertiary structures that combines b and analysis by curve-fitting of original spectra with protein thermal dena turation is described in detail. The assignment of IR protein bands in H2O and in D2O, one of the more difficult points in protein IR spectroscopy, is also reviewed, including some cases of unclear assignments such as loops, beta-hairpins, or 3(10)-helices. The review includes monographic studies of some membrane proteins whose structure and function have been analysed in detail by IR spectroscopy. Special emphasis has been made on the role of su bunit III in cytochrome c oxidase structure, and the proton pathways across this molecule, on the topology and functional cycle of sarcoplasmic reticu lum Ca2+-ATPase, and on the role of lipids in determining the structure of the nicotinic acetylcholine receptor. In addition, shorter descriptions of retinal proteins and references to other membrane proteins that have been s tudied less extensively are also included. (C) 1999 Elsevier Science Ltd. A ll rights reserved.