title: Role of the conserved distal heme asparagine of coral allene oxide synthase (Asn137) and human catalase (Asn148): mutations affect the rate but not the essential chemistry of the enzymatic transformations.
abstract: A catalase-related allene oxide synthase (cAOS) and true catalases that metabolize hydrogen peroxide have similar structure around the heme. One of the distal heme residues considered to help control catalysis is a highly conserved asparagine. Here we addressed the role of this residue in metabolism of the natural substrate 8R-hydroperoxyeicosatetraenoic acid by cAOS and in H(2)O(2) breakdown by catalase. In cAOS, the mutations N137A, N137Q, N137S, N137D, and N137H drastically reduced the rate of reaction (to 0.8-4% of wild-type), yet the mutants all formed the allene oxide as product. This is remarkable because there are many potential heme-catalyzed transformations of fatty acid hydroperoxides and special enzymatic control must be required. In human catalase, the N148A, N148S, or N148D mutations only reduced rates to approximately 20% of wild-type. The distal heme Asn is not essential in either catalase or cAOS. Its conservation throughout evolution may relate to a role in optimizing catalysis.
authors.affiliation: Department of Pharmacology and Vanderbilt Institute of Chemical Biology, Vanderbilt University, 23rd Avenue at Pierce, Nashville, TN 37232-6602, USA.
authors.forename: Benlian
authors.initials: B
authors.lastname: Gao
authors.forename: William E
authors.initials: WE
authors.lastname: Boeglin
authors.forename: Alan R
authors.initials: AR
authors.lastname: Brash
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D037421:Anthozoa / Q000201:enzymology*; D001216:Asparagine / Q000737:chemistry*; D002374:Catalase / Q000737:chemistry*; D017124:Conserved Sequence; D004789:Enzyme Activation; D004795:Enzyme Stability; D006418:Heme / Q000737:chemistry*; D006801:Humans; D019746:Intramolecular Oxidoreductases / Q000737:chemistry*; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D013045:Species Specificity; D013329:Structure-Activity Relationship
chemical_list: D006418:Heme; D001216:Asparagine; D002374:Catalase; D019746:Intramolecular Oxidoreductases; C021377:hydroperoxide isomerase