Subsystem: Molybdenum cofactor biosynthesis
This subsystem's description is:
Molybdenum is an essential trace element in the form of molybdenum cofactor (Moco) which is associated with the metabolism of nitrogen, carbon and sulfur by redox active enzymes. Moco contains a tricyclic pyranopterin, termed molybdopterin (MPT). MoeA, together with MoaB, is responsible for the metal incorporation into MPT, the third step in Moco biosynthesis. MPT carries the cis-dithiolene group responsible for molybdenum ligation. This dithiolene group is generated by MPT synthase in the second major step in Moco biosynthesis. MPT synthase is a heterotetramer consisting of two large (MoaE) and two small (MoaD) subunits. The small subunit 2xMoaD) is inserted into the lare subunit (2xMoaE) to form the active site. The small subunit, which is structurally similar to ubiquitin, contains a C-terminal thiocarboxylated glycine residue that serves as a sulfur donor for the synthesis of the MPT dithiolene group. MoaC, a small hexameric protein, converts, together with MoaA, a guanosine derivative to the precursor Z by inserting the carbon-8 of the purine between the 2' and 3' ribose carbon atoms, which is the first of three phases of Moco biosynthesis. (bacterial MoaA NOT archaeal MoaA) MoaB shows high similarity to MogA, but little is known about its physiological role. MoeB, like ThiF, begins with a nucleophilic attack of the C-terminal carboxylate of MoaD and ThiS, respectively, on the alpha-phosphate of an ATP molecule bound at the active site of the activating enzymes, leading to the formation of a high-energy acyladenylate intermediate and subsequently to the formation of a thiocarboxylate at the C termini of MoaD and ThiS. MPT can be further modified by attachment of a GMP group to the terminal phosphate of MPT to form molybdopterin guanine dinucleotide (MGD). This GMP attachment step is catalyzed by MobA, by linking a guanosine 5'-phosphate to MPT forming molybdopterin guanine dinucleotide. This reaction requires GTP, MgCl2, and the MPT form of the cofactor. It is a reaction unique to prokaryotes?
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|Diagram||Functional Roles||Subsystem Spreadsheet||Description||Additional Notes|
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