Nitric oxide (NO) is a signalling molecule involved in a range of diseases and conditions, such as asthma, cancer and impotence. The natural levels of arginine derivates — which can inhibit nitric oxide synthase and decrease NO — are controlled in part by dimethylarginine dimethylaminohydrolase (DDAH). In August Nature Structural Biology Judith Murray-Rust and colleagues from the School of Crystallography, Birkbeck College, London report the structure of the enzyme DDAH that may offer a new way of indirectly decreasing NO concentrations.

Murray-Rust et al. identified the crystal structure of a Pseudomonas aureus DDAH and found that this enzyme is a member of a structural superfamily of enzymes that use arginine or substituted arginine as a substrate. The identification of a Cys-His-Glu catalytic triad and the structures of a Cys to Ser point mutant bound to both substrate and product suggest a common reaction mechanism between DDAH and other superfamily members...