Proteins in motion: resonance Raman spectroscopy as a probe of functional intermediates

Elucidating proteins function at a level that allows for intelligent design and manipulation is essential in realization of their potential role in biomedical and industrial applications. It has become increasingly apparent though, that probing structures and functionalities under equilibrium conditions is not sufficient. Rather, many aspects of protein behavior and reactivity are rooted in protein dynamics. Thus, there is a growing effort to probe intermediate structures that occur transiently during the course of a proteins function in particular linked to the binding or release of a ligand or substrate. However, studies following the sequence of conformational changes triggered by the binding of substrate/ligand and the concomitant change in functional properties are inherently difficult because often the diffusion times are of the order of conformational relaxation times. This chapter describes methodologies for generating resonance Raman spectra from transient forms of hemoglobin under conditions that allow for the systematic exploration of conformational relaxation and functionality. Special consideration is given to Raman compatible protocols based on sol-gel encapsulation that allow for the preparation, trapping and temporal tuning of nonequilibrium population generated from either the addition or the removal of ligands/substrates.