Structural aspects of mononuclear Mo/W-enzymes

This review provides an overview of the contributions of protein X-ray crystallography to the field of pyranopterin-containing W/Mo-enzymes. Several crystal structures for all of the four different families of pyranopterin-containing enzymes have been determined in recent years allowing one to compare overall folds and active site architectures. Especially within the dimethylsulfoxide reductase family and the Mo-containing hydroxylases a diversity of Mo/W-ligands has been discovered, challenging the earlier proposed functions of individual active site components. Reinterpretations of structures and the use of enzyme variants and complexes with inhibitors and slow substrate provided further insights, which will be discussed for the individual enzymes.