Institut für Mikrobiologie, Technische Universität Braunschweig, Spielmannstr 7, 38106 Braunschweig, Germany.
Institut für Organische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.
Archaea. 2014 Jan 23;2014:327637. doi: 10.1155/2014/327637. eCollection 2014.
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 from Methanosarcina barkeri were functionally characterized. Using an in vivo enzyme 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 III in vivo. Finally, recombinant AhbD (Mbar_A1458) was produced in E. coli and purified indicating that this protein most likely contains two [4Fe-4S] clusters. Using an in vitro enzyme activity assay it was demonstrated that AhbD catalyzes the conversion of iron-coproporphyrin III into heme.
在生命体中，血红素由共同的前体尿卟啉原 III 通过两种截然不同的途径中的任一种形成。与采用所谓的“经典”血红素生物合成途径的真核生物和大多数细菌不同，古菌使用替代途径。在这条途径中，血红素由尿卟啉原 III 通过中间产物原卟啉-2、硅氢化血红素、硅血红素、12,18-二脱羧硅血红素和铁-羧原卟啉 III 形成。在这项研究中，从 Methanosarcina barkeri 中功能性地鉴定了血红素生物合成蛋白 AhbAB、AhbC 和 AhbD。通过体内酶活性测定表明，AhbA 和 AhbB（Mbar_A1459 和 Mbar_A1460）共同催化硅血红素转化为 12,18-二脱羧硅血红素。这两种蛋白质形成异二聚体复合物，可能受到途径终产物血红素的反馈调节。此外，AhbC（Mbar_A1793）被证明能够在体内催化铁-羧原卟啉 III 的形成。最后，在大肠杆菌中产生并纯化了重组 AhbD（Mbar_A1458），表明该蛋白很可能含有两个[4Fe-4S]簇。通过体外酶活性测定表明，AhbD 催化铁-羧原卟啉 III 转化为血红素。
