Structure of Catalases

Abstract

Catalase (hydrogen peroxide: hydrogen peroxide oxidoreductase, EC 1.11.1.6) is found in virtually all aerobic organisms. It employs a two-electron-transfer mechanism to disproportionate hydrogen peroxide into molecular oxygen and water (Deisseroth and Dounce 1970). These enzymes serve, in part, to protect the cell from the toxic effects of small peroxides. However, the entire range of biological functions of catalases remains unclear. Two types of catalases are known: Mn-catalases and heme-containing catalases. Mn-catalases, only present in certain prokaryotes, are non-heme hexameric enzymes with an “all-α” fold (Barynin et al. 1986). In contrast, heme-containing catalases, which are widespread, are homotetramers with molecular weights ranging from about 200,000 to 350,000. The three-dimensional crystal structures of five of these heme-containing catalases (Table 1) have been reported at almost atomic resolution. These include members from two eukaryote and from three prokaryote catalases: (1) from the fungus Penicillium vitale (PVC) (Vainshtein et al. 1981Vainshtein et al. 1986; G. Murshudov et al., unpubl.); (2) the mammalian catalase from beef liver (BLC) (Murthy et al. 1981; Fita et al. 1986); (3) from Micrococcus lysodeikticus (MLC) (Murshudov et al. 1992 and unpubl.), (4) from a peroxide-resistant mutant of Proteus mirabilis (PMC_PR) (Gouet et al. 1995); and (5) HPII catalase from E. coli (Bravo et al. 1995). The α+β fold of the subunits and the molecular organization in all these heme catalase structures are unique among proteins and, in particular, present striking differences from heme peroxidases. In catalases the four heme groups are deeply buried inside the molecule due to complex intersubunit interactions...