Conformational Change in Native Proteins

Using a variety of more conventional techniques, Moore and Williams assigned resonances to 39 aromatic protons and 8 aliphatic protons in ferrocyto-chrome c. Further studies on the effect of oxidation, pH, and temperature showed that the molecule is relatively rigid at the centre compared with the flexibility observed at the surface. Only small conformational changes were observed on oxidation except in the region around L-isoleucine-S7 which became relatively mobile. 

Nagayama, P. Bachman, R. R. Ernst, and K. Wiithrich, Biochem. Biophys. Res. Commun.. 1979,86,218. 

The precise conformation of structure around the metal cofactors of metallo-proteins has been studied by. f-ray absorption fine edge spectroscopy (EXAFS). Oxidized and reduced cytochrome c were studied and no significant difference was observed. In view of the n.m.r. evidence this finding was interpreted as evidence for there being a shift from a rigid structure in the reduced state to a flexible conformer in the oxidized state having the same time-averaged atomic co-ordinates around the haem as ferrocytochrome c. 

The influence of the protein component of cytochrome c on the haem has also been investigated with the new technique of Raman difference spectroscopy. The basis of the method is similar to conventional difference spectroscopy and the resolution of the haem resonance has been increased S-fold. The method has also been used to study structural changes in methaemoglobin. Williams et a/. have used numerical methods to produce and interpret Raman difference spectra. These workers subtracted solvent spectra from protein spectra and showed that the amide I Raman scattering intensity could be used to define helix, sheet, and reverse turns with unparalleled accuracy. The method depends on computing reference spectra for each variety of secondary structure and fitting these in linear combination to the observed spectrum. The same technique has also been successfully applied to the amide III spectrum of proteins in deuterium oxide.  

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