InterPro domain: IPR000343

This entry represents glutamyl-tRNA reductase ( 1.2.1.70 ), which required NADPH as a coenzyme [ 1 , 2 ]. This entry also includes the multifunctional siroheme biosynthesis protein HemA from Clostridium josui which besides acting as a glutamyl-tRNA reductase also converts precorrin-2 to sirohydrochlorin and sirohydrochlorin to siroheme [ 3 ].

Delta-aminolevulinic acid (ALA) is the obligatory precursor for the synthesis of all tetrapyrroles including porphyrin derivatives such as chlorophyll and heme. ALA can be synthesized via two different pathways: the Shemin (or C4) pathway which involves the single step condensation of succinyl-CoA and glycine and which is catalyzed by ALA synthase and via the C5 pathway from the five-carbon skeleton of glutamate. The C5 pathway operates in the chloroplast of plants and algae, in cyanobacteria, in some eubacteria and in archaebacteria [ 4 ].

The initial step in the C5 pathway is carried out by glutamyl-tRNA reductase (GluTR) which catalyzes the NADP-dependent conversion of glutamate- tRNA(Glu) to glutamate-1-semialdehyde (GSA) with the concomitant release of tRNA(Glu) which can then be recharged with glutamate by glutamyl-tRNA synthetase [ 4 ].

1. Biosynthesis of cobalamin (vitamin B12): a bacterial conundrum. Cell. Mol. Life Sci. 57, 1880-93
2. Glutamyl-transfer RNA: a precursor of heme and chlorophyll biosynthesis. Trends Biochem. Sci. 17, 215-8
3. Cloning and sequencing of some genes responsible for porphyrin biosynthesis from the anaerobic bacterium Clostridium josui. J. Bacteriol. 177, 5169-75