Electron crystallography reveals amino acid charges

Yonekura, K. et al. Proc. Natl. Acad. Sci. USA. doi:10.1073/pnas.1500724112 (17 February 2015).

Electron crystallography of three-dimensional protein crystals is an emerging technique in structural biology. Electron crystallography may be useful for studying weakly diffracting or thin crystals, as electrons are scattered 4–5 orders of magnitude more strongly than X-rays. Yonekura et al. describe a method for electron crystallographic analysis of ultrathin protein crystals. They developed a new diffractometer for data collection on thin protein crystals as well as a set of programs for data analysis. Using this method, they solved the atomic structures of a Ca²⁺-dependent ATPase and catalase. Because electron crystallography yields Coulomb potential maps rather than electron density maps, the charged states of amino acids in the Ca²⁺-dependent ATPase active site and the iron atom in catalase could be determined, yielding new insights into these proteins.