Binding of 5-GTP to the C-terminal FeS Cluster of the Radical S-Adenosylmethionine Enzyme MoaA Provides Insights into its Mechanism
The first step in molybdenum cofactor biosynthesis, the conversion of 5'-GTP to precursor Z, an oxygen-sensitive tetrahydropyranopterin is catalyzed by the S-adenosylmethionine (SAM)-dependent enzyme MoaA and the accessory protein MoaC. This reaction involves the radical-initiated intramolecular rearrangement of the guanine C8 atom. MoaA harbors an N-terminal [4Fe-4S] cluster, which is involved in the reductive cleavage of SAM and generates a 5'-deoxyadenosyl radical (5'-dA), and a C-terminal [4Fe-4S] cluster presumably involved in substrate binding and/or activation. Biochemical studies identified residues involved in 5'-GTP binding and the determinants of nucleotide specificity. The crystal structure of MoaA in complex with 5'-GTP confirms the biochemical data and provides valuable insights into the subsequent radical reaction. MoaA binds 5'-GTP with high affinity and interacts through its C-terminal [4Fe-4S] cluster with the guanine N1 and N2 atoms, in a yet uncharacterized binding mode. The tightly anchored triphosphate moiety prevents the escape of radical intermediates. This structure also visualizes the L-Met and 5'-dA cleavage products of SAM. Rotation of the 5'-dA ribose and/or conformational changes of the guanosine are proposed to bring the 5'-deoxyadenosyl radical into close proximity of either the ribose C2' and C3' or the guanine C8 carbon atoms leading to hydrogen abstraction.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 914306
- Report Number(s):
- BNL-78874-2007-JA; PNASA6; TRN: US0802849
- Journal Information:
- Proc Natl Acad Sci USA, Vol. 103; ISSN 0027-8424
- Country of Publication:
- United States
- Language:
- English
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