Extended X-ray absorption fine structure of the [Fe]-hydrogenase Hmd active site

Hydrogenases are enzymes that catalyze the reversible oxidation of molecular hydrogen. Although their structure and catalytic mechanism are of considerable applied interest as models for the development of efficient catalysts for hydrogen fueled processes, the understanding of how hydrogenases react with H2 is only in its infancy. Two of the three known types of hydrogenases are iron-sulfur proteins that contain a dinuclear metal center, either [NiFe] or [FeFe]. In contrast, [Fe]-hydrogenase is the only mononuclear hydrogenase and thus a perfect system for studying the structural and electronic determinants of these enzymes. Here we summarize recent improvements in modeling based on the EXAFS signal and the geometric structure of this metalloenzyme in its as isolated or reconstituted form. The individual contributions to the EXAFS resulting in two different structural models are presented and discussed. Inspired by the new crystal structure, we show an advanced EXAFS model for the enzyme from Methanothermobacter marburgensis.