Monitoring protein assembly using quasielastic light scattering spectroscopy.

This article discussed the principles and practice of QLS with respect to protein assembly reactions. Particles undergoing Brownian motion in solution produce fluctuations in scattered light intensity. We have described how the temporal correlation function of these fluctuations can be measured and how mathematical analysis of the correlation function provides information about the distribution of diffusion coefficients of the particles. We have explained that deconvolution of the correlation function is an "ill-posed" problem and therefore that careful attention must be paid to the assumptions incorporated into data analysis procedures. We have shown how the Stokes-Einstein relationship can be used to convert distributions of diffusion coefficients into distributions of particle size. In the case of fibrillar polymers, this process allows direct determination of fibril length, enabling nucleation and elongation rates to be calculated. Finally, we have used examples from studies of A beta fibrillogenesis to illustrate the power these quantitative capabilities provide for understanding the molecular mechanisms of the fibrillogenesis reaction and for guiding the development of fibrillogenesis inhibitors.