XFEL structure of carbonic anhydrase II: a comparative study of XFEL, NMR, X-ray and neutron structures.

The combination of X-ray free-electron lasers (XFELs) with serial femtosecond crystallography represents cutting-edge technology in structural biology, allowing the study of enzyme reactions and dynamics in real time through the generation of `molecular movies'. This technology combines short and precise high-energy X-ray exposure to a stream of protein microcrystals. Here, the XFEL structure of carbonic anhydrase II, a ubiquitous enzyme responsible for the interconversion of CO2 and bicarbonate, is reported, and is compared with previously reported NMR and synchrotron X-ray and neutron single-crystal structures.

Neutron crystallographic studies of carbonic anhydrase.

The carbonic anhydrases (CAs; EC 4.2.1.1) are a family of metalloenzymes that catalyze the reversible hydration of carbon dioxide (CO2) and bicarbonate (HCO3-). Since their discovery in 1933, CAs have been at the forefront of scientific discovery: the understanding of enzymatic reactions, structural biology, molecular dynamics, drug discovery, and clinical medicine. These ubiquitous enzymes equilibrate the reaction between CO2, HCO3-, and protons. Hence, CAs have important roles in ion transport, acid-base regulation, gas exchange, photosynthesis, and CO2 fixation. In this chapter, we describe the protocols leading to, and the analysis of CA neutron crystal structures. This accumulation of structural knowledge adds to our understanding of the enzymatic mechanism and development of CA inhibitors.