Linear dichroism of fibrous proteins

Protein and peptide fibres are implicated in many diseases including Alzheimer’s and Creutzfeldt-Jakob Disease (CJD). In order to test for binding of potential drugs to these and other fibrous proteins, one can employ LD. This will not only indicate ligands that bind to protein fibres, but also give information on the orientation of the ligand relative to the fibre axis. As well as formation of protein fibres in disease, fibres are formed during many normal cellular processes. One example of this is during cell division where FtsZ (a tubulin homologue) reversibly polymerises upon GTP binding. We can follow this process by LD, gaining information on both the kinetics of the process and the orientation of the protein monomers in the fibrous forms.

Actin was the first fibrous protein to be studied by Couette flow LD and recently we have improved the quality of data one can collect for such a system and also devised a range of new experiments. It is therefore an ideal case study to show possibilities of LD of fibrous proteins. Some examples of LD data are given below. The papers which summarise the work give more details.

UV LD spectra showing the apparent shift to shorter wavelength of the maximum signal as the concentration of F-actin is reduced. It is important to check for light scattering and high absorbance at low wavelengths. The true spectrum is shown in bold.

One can probe interactions between protein fibers and other molecules including proteins, drugs other small molecules.