title: The hemA gene encoding glutamyl-tRNA reductase from the archaeon Methanobacterium thermoautotrophicum strain Marburg.
abstract: In archaea the first general tetrapyrrole precursor 5-aminolevulinic acid (ALA) is formed via the tRNA-dependent five-carbon pathway from glutamate. We have cloned the hemA gene encoding the central enzyme of the pathway glutamyl-tRNA reductase from the methanogenic archaeon Methanobacterium thermoautotrophicum by complementation of an Escherichia coli hemA mutant to ALA prototrophy. An 1194 bp open reading frame that encodes a 398 amino acid polypeptide with the calculated M, 44,509 was detected. The deduced amino acid sequence showed 20-35% amino acid identity to bacterial HemAs with the highest identity score to the Pseudomonas aeruginosa HemA. An identity of approximately 22% was found to plant HemAs. Glutamyl-tRNA reductase activity was shown for the M. thermoautotrophicum HemA after overexpression in E. coli and partial purification. The enzymatic reaction catalyzed by the partially purified enzyme revealed a temperature optimum of 65 degrees C at an optimal pH of 7.0. The reductase utilized preferentially NADPH for the reduction of the activated carboxyl group. The presence of ATP and GTP showed no obvious influence on catalysis.
authors.affiliation: Laboratorium für Mikrobiologie des Fachbereich Biologie der Philipps-Universität, Marburg, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Hungerer
authors.forename: D S
authors.initials: DS
authors.lastname: Weiss
authors.forename: R K
authors.initials: RK
authors.lastname: Thauer
authors.forename: D
authors.initials: D
authors.lastname: Jahn
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000737:chemistry / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D004926:Escherichia coli; D017014:Methanobacterium; D008969:Molecular Sequence Data; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D012346:RNA, Transfer, Amino Acyl; D000445:Aldehyde Oxidoreductases; C067282:glutamyl tRNA reductase