The Alternative Route to Heme in the Methanogenic ArchaeonMethanosarcina barkeri

[摘要] In living organisms heme is formed from the common precursor uroporphyrinogen III by either one of two substantially different pathways. In contrast to eukaryotes and most bacteria which employ the so-called “classical” heme biosynthesis pathway, the archaea use an alternative route. In this pathway, heme is formed from uroporphyrinogen III via the intermediates precorrin-2, sirohydrochlorin, siroheme, 12,18-didecarboxysiroheme, and iron-coproporphyrin III. In this study the heme biosynthesis proteins AhbAB, AhbC, and AhbD fromMethanosarcina barkeriwere functionally characterized. Using anin vivoenzyme activity assay it was shown that AhbA and AhbB (Mbar_A1459 and Mbar_A1460) together catalyze the conversion of siroheme into 12,18-didecarboxysiroheme. The two proteins form a heterodimeric complex which might be subject to feedback regulation by the pathway end-product heme. Further, AhbC (Mbar_A1793) was shown to catalyze the formation of iron-coproporphyrin IIIin vivo. Finally, recombinant AhbD (Mbar_A1458) was produced inE. coliand purified indicating that this protein most likely contains two [4Fe-4S] clusters. Using anin vitroenzyme activity assay it was demonstrated that AhbD catalyzes the conversion of iron-coproporphyrin III into heme.

[学科分类] 微生物学和免疫学