The hemA gene encoding glutamyl-tRNA reductase from the archaeon Methanobacterium thermoautotrophicum strain Marburg

✍ Scribed by Christoph Hungerer; David S. Weiss; Rudolf K. Thauer; Dieter Jahn

• Book ID: 103992315
• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 665 KB
• Volume: 4
• Category: Article
• ISSN: 0968-0896
• DOI: 10.1016/0968-0896(96)00098-3

✦ Synopsis

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.