Measurement of the Raman optical activity (ROA) spectra of biomolecules
has become an experimental possibility due to significant advances in the available
technology, and its successful implementation into the ROA instruments at the
University of Glasgow. The ease with which the ROA spectra of biological molecules
can be successfully measured lends itself perfectly to the ever-growing demand for
biomolecular structural information, especially in the context of proteomics and the
Human Genome Project. ROA spectroscopy is able to probe the chiral peptide
backbone of proteins, and as such the ROA spectrum of a protein contains a wealth of
structural information from within the whole molecule, across the whole vibrational
spectrum. As well as containing detailed information from specific structural elements
such as sections of secondary structure and motifs, the ability of ROA to see the
molecule as a whole also enables the global fold of the protein to be deduced from the
ROA spectrum.
The development of the analysis of ROA spectra has largely been based upon
the correlation of ROA spectra of proteins of known structure with structural
information from alternative sources, chiefly X-ray crystallography and
multidimensional nuclear magnetic resonance (NMR). As the database of ROA
spectra of polypeptides and proteins has grown, it has been possible to tighten up the
assignment of ROA spectral bands and band patterns to aspects of known structural
content. With a basis for the correlation between the ROA spectrum and the known
crystal structure (or NMR structure) being well established, it is possible to interpret
the ROA spectra of proteins that do not have (for whatever reason) well defined
structures. This means that ROA spectroscopy can provide invaluable structural
information for proteins that are precluded from analysis by other techniques, and also
cast new light on the structures of proteins that have not been well defined.
In order to fully interpret an ROA spectrum of a protein, it is necessary to be
familiar with protein structure and the ROA experiment as a whole. Analysing an
ROA spectrum is a detailed and highly subjective process. Depending on the
experience of the analyst, the information contained within the spectra can be extracted readily or not so readily. For this reason, it would be desirable to develop a
technique that is capable of interpreting not only individual spectra, but also whole
data sets in a manner that is independent of the analyst, and therefore independent of
any preconceptions (or inexperience) the analyst may have.
This project presents an up-to-date collection of newly obtained ROA spectra
of a large number of proteins across a range of structural class types. In addition, the
statistical technique of principal component analysis (PflA) has been used as a tool
for the analysis of this new data. It is hoped that the result of this work will provide a
basis for the future analysis of protein ROA spectra that is both mathematically
rigorous and convenient
