Identification of the site of oxidase substrate binding in Scytalidium thermophilum catalase.

The catalase from Scytalidium thermophilum is a homotetramer containing a heme d in each active site. Although the enzyme has a classical monofunctional catalase fold, it also possesses oxidase activity towards a number of small organics, including catechol and phenol. In order to further investigate this, the crystal structure of the complex of the catalase with the classical catalase inhibitor 3‐amino‐1,2,4‐triazole (3TR) was determined at 1.95 Å resolution. Surprisingly, no binding to the heme site was observed; instead, 3TR occupies a binding site corresponding to the NADPH‐binding pocket in mammalian catalases at the entrance to a lateral channel leading to the heme. Kinetic analysis of site‐directed mutants supports the assignment of this pocket as the binding site for oxidase substrates. [ABSTRACT FROM AUTHOR]