Multifunctional enzyme that catalyzes the NADPH-dependent reduction of glutamyl-tRNA(Glu) to glutamate 1-semialdehyde (GSA), the NAD-dependent ring dehydrogenation of precorrin-2 to sirohydrochlorin and finally, the ferrochelation of sirohydrochlorin to yield siroheme. (S)-4-amino-5-oxopentanoate + NADP(+) + tRNA(Glu) = H(+) + L-glutamyl-tRNA(Glu) + NADPH NAD(+) + precorrin-2 = 2 H(+) + NADH + sirohydrochlorin 2 H(+) + siroheme = Fe(2+) + sirohydrochlorin Cofactor biosynthesis; adenosylcobalamin biosynthesis; sirohydrochlorin from precorrin-2: step 1/1. Porphyrin-containing compound metabolism; siroheme biosynthesis; siroheme from sirohydrochlorin: step 1/1. Porphyrin-containing compound metabolism; siroheme biosynthesis; sirohydrochlorin from precorrin-2: step 1/1. Porphyrin-containing compound metabolism; protoporphyrin-IX biosynthesis; 5-aminolevulinate from L-glutamyl-tRNA(Glu): step 1/2. Homodimer. Possesses an unusual extended V-shaped dimeric structure with each monomer consisting of three distinct domains arranged along a curved 'spinal' alpha-helix. The N-terminal catalytic domain specifically recognizes the glutamate moiety of the substrate. The second domain is the NADPH-binding domain, and the third C-terminal domain is responsible for dimerization. During catalysis, the active site Cys acts as a nucleophile attacking the alpha-carbonyl group of tRNA-bound glutamate with the formation of a thioester intermediate between enzyme and glutamate, and the concomitant release of tRNA(Glu). The thioester intermediate is finally reduced by direct hydride transfer from NADPH, to form the product GSA. In the N-terminal section; belongs to the glutamyl-tRNA reductase family. In the C-terminal section; belongs to the precorrin-2 dehydrogenase / sirohydrochlorin ferrochelatase family.