Damage-free Electronic and Geometric Structure Determination of Metalloproteins
Proteins are essential parts of biological organisms, functioning, for example, as enzymes in chemical reactions, antibodies or as structural components. Metalloproteins, in particular, where one or various metal ions are at the catalytic center of the enzyme, perform a vast number of important functions in nature, including electron transfer processes and chemical transformations. Understanding how these mechanisms work is essential for many different areas, as such knowledge could help to (a) improve natural systems by designing specific substrates, inhibitors or enhancers, and (b) improve the design of synthetic systems that mimic key features found in nature. These systems can be inquired in novel ways with X-ray free electron lasers (XFELs) by using the probe-before-destroy approach to study biological redox active centers under functioning conditions, and by performing pump-probe studies down to sub 100 fs time resolution. In this chapter, we will describe the new methods developed within the last few years at XFELs and provide an inclusive review of the experiments done on metalloproteins at the existing XFELs with an emphasis on our work on the structure and function of photosystem II, targeted toward understanding the reaction mechanism of light induced water oxidation in oxygenic photosynthesis.