Ž . Journal of Molecular Catalysis B: Enzymatic 7 1999 207–221 www.elsevier.comrlocatermolcatb FTIR spectroscopic characterization of protein structure in aqueous and non-aqueous media Parvez I. Haris a, ) , Feride Severcan b a Department of Biological Sciences, De Montfort UniÕersity, Hawthorn Building, The Gateway, Leicester LE1 9BH, UK b Molecular Biology–Biotechnology Research Unit, Department of Biology, Middle East Technical UniÕersity, 06531 Ankara, Turkey Abstract With increasing use of proteins in many different applications, ranging from phramaceuticals to biosensors and biomaterials, there has emerged a need for protein structural characterisation in diverse environments. In many cases it is not sufficient to just have the three-dimensional structure of a protein in H O or in the crystalline state. Often information on the 2 structural properties of a protein is required in the presence of organic solvents, detergent micelles, phospholipid membranes Ž . and so on. Fourier transform infrared spectroscopy FTIR has been identified as one of the few techniques that can be applied for structural characterisation of proteins in such environments. Here we discuss how this technique is being used to obtain information on protein structure and stability in both aqueous and non-aqueous media. Examples are drawn from our studies of water soluble proteins and membrane proteins. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Infrared spectroscopy; FTIR spectroscopy; Protein conformation; Protein stability; Protein folding; Protein secondary structure; Membrane proteins 1. Introduction With the progress in sequencing of the hu- man genome, the disparity between the number of known sequences and the number of experi- mentally determined protein structures contin- ues to increase. Consequently, there is a clear demand for development of techniques for rapid structural characterisation of the encoded pro- teins. X-ray crystallography and nuclear mag- Ž . netic resonance NMR spectroscopy provide the complete three-dimensional structure of a protein and are by far the most powerful tech- AbbreÕiations: FTIR, Fourier transform infrared spectroscopy; NMR, Nuclear magnetic resonance spectroscopy ) Corresponding author. E-mail: pharis@dmu.ac.uk niques available to structural biochemists. Al- though X-ray crystallography is an excellent technique for the determination of three-dimen- sional structure of proteins it has the following disadvantages: crystallographic studies require high-quality single crystals which are not avail- able for many proteins such as most of the membrane proteins, and the structure of a pro- tein in a crystal may not always relate to its structure in solution. X-ray diffraction data pre- sents a static picture of protein structure which does not represent the protein conformation with its dynamic nature in biological systems. The slowness of the procedure is the other disadvan- tage of the technique. NMR spectroscopy has better flexibility to study protein structure in solution. However, the interpretation of NMR 1381-1177r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S1381-1177 99 00030-2