Binding of 5'-GTP to the C-terminal FeS cluster of the radical S-adenosylmethionine enzyme MoaA provides insights into its mechanismHaenzelmann, P., Schindelin, H.
(2006) Proc Natl Acad Sci U S A 103: 6829-6834
- PubMed: 16632608
- DOI: https://doi.org/10.1073/pnas.0510711103
- Primary Citation of Related Structures:
- PubMed Abstract:
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.
Department of Biochemistry and Center for Structural Biology, Stony Brook University, Stony Brook, NY 11794-5215, USA. firstname.lastname@example.org