Nanosecond time-resolved polarization spectroscopies and applications to the study of protein function and folding

摘要

Sensitive optical methods developed over the past decade make it possible to monitor the dynamics of structural changes in proteins-changes which can, for instance, modulate function in allosteric proteins or mark self-assembly toward the functional, native structure in protein folding-by using linearly or elliptically polarized light to perform nanosecond spectral measurements. The ellipsometric approach to time-resolved circular dichroism (TRCD) spectroscopy, initially limited to near-UV-visible single-wavelength measurements with 50-100 ns time resolution, has been extended to allow for multichannel spectral measurements, expansion of the spectral range into the far UV, and refinement of the time resolution to 1 ns. The ellipsometric technique has also been extended to magnetically induced TRCD (TRMCD) measurements, while the development of closely related polarimetric techniques has made available nanosecond time-resolved linear dichroism (TRLD) and optical rotatory dispersion (TRORD) spectral measurements with high sensitivity. The sensitivity of the polarimetric TRLD method, for instance, is about two orders of magnitude greater than that of standard approaches. Applications of these techniques to the study of function in a number of proteins, including myoglobin, hemoglobin, and cytochrome c oxidase, and applications to the study of folding kinetics in peptides and proteins are discussed.