The development of aerobic life on earth strictly depended on the evolution of enzymatic systems able to efficiently degrade reactive oxygen species like hydrogen peroxide and superoxide radical anions. Catalases, for example, provided a strategy to disproportionate hydrogen peroxide into water and dioxygen. Cellular hydrogen peroxide levels are also reduced by peroxidases, which utilize an additional peroxidatic pathway involving a one-electron donor instead of a second equivalent of hydrogen peroxide to return to the ground state. Typical catalases are tetrameric with one heme group per subunit and native molecular masses around 250 kDa, while most non-mammalian peroxidases are monomers consisting of a common 10-helical core around the heme group. The reactivity of heme-containing hydrogen peroxide converting enzymes is largely determined by the architecture of the heme proximal and distal sides. Heme proximal ligands typically comprise histidine, cysteine and tyrosine residues carrying a partial or full negative charge to stabilize the ferric iron versus the ferrous iron. The heme distal side is responsible for the interaction with the substrates and facilitates the binding of hydrogen peroxide, the heterolysis of the O–O bond, and the stabilization of oxo-ferryl intermediates. A coordination of the heme iron by tyrosine trans to an empty coordination is supposed to be a unique feature of mono-functional heme-containing catalases and the close structural relative coral allene oxidase. Here you can see a crystal structure of the novel heme-containing protein from Silicibacter pomeroyi, a lithoheterotrophic α-proteobacterium which supplements heterotrophy by metabolizing carbon monoxide and sulphide (PDB code: 2OYY)

#molecularart ... #catalase ... #heme ... #hexameric ... #Silicibacter ... #xray

Structure rendered with @proteinimaging and depicted with @corelphotopaint