Substrate binding by a vanadium-bromoperoxidase investigated by XAFS at the Br K-edge

Some marine and terrestrial organisms produce halogenated compounds which exhibit antibiotic activity to, presumably, counteract bacterial attacks. The biosynthesis of these halogenated compounds involves haloperoxidases, which are heme-type or vanadate-dependent metalloproteins. Vanadate-dependent haloperoxidases have been found in brown algae (e.g., in Ascophyllum nodosum), red algae, a lichen species and lower fungi (e.g., in Curvularia inaequalis). The active form of the vanadium haloperoxidase contains a single vanadium atom per 60 kDa subunit. Haloperoxidases catalyze the formation of hypohaleous acid starting from halide ions and hydrogen peroxide (Hal- + H+ + H2O2-> HOHal + H2O with Hal = Cl, Br, I). Haloperoxidases have been used for anti-bacterial medicamentation; utilization as catalysts for in-vitro oxidation of organic compunds are discussed [1, 2]. Recently, atomic resolution structures of the active form of the vanadate-dependent bromo-peroxidase from A. nodosum [3] and of a similar chloroperoxidase (including its peroxo derivative) from C. inaequalis became available [4]. However, the type of interaction between the active site vanadium and the substrate, the halide, remained essentiall