Raman Difference Studies of Protein Structure and Folding, Enzymatic Catalysis and Ligand Binding

Raman difference spectroscopy (RDS) can be employed successfully and generally to overcome the problem of spectral crowding in Raman measurements of large macromolecules, such as proteins. In such an experiment, a protein is 'tagged' in some way and the difference spectrum between the protein and its modified version is measured, often by using isotope editing techniques. Subtraction of the two spectra yields the spectrum of those parts of the protein which have been tagged. In this way, the RDS spectrum contains an interpretable number of bands. RDS techniques are developed in this paper. Some recent results using Raman difference spectroscopy on the structures of proteins and protein complexes with small molecules are discussed to illustrate the technique. Two areas have been of special interest, one concerning how proteins bind ligands enzymatic catalysis, and the other concerning the structure of proteins and how they assemble themselves into their specific biologically active shape from a disordered polypeptide chain. In addition, the interpretations of RDS spectra in terms of structure and function are outlined.