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.
Hänzelmann
Petra
P
Department of Biochemistry and Center for Structural Biology, Stony Brook University, Stony Brook, NY 11794-5215, USA. petra@csb.sunysb.edu
Schindelin
Hermann
H
D001665:Binding Sites; D003067:Coenzymes / Q000096:biosynthesis; D018360:Crystallography, X-Ray; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism*; D006867:Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008667:Metalloproteins / Q000096:biosynthesis; D008958:Models, Molecular; D015394:Molecular Structure; D000090006:Molybdenum Cofactors; D011487:Protein Conformation; D011621:Pteridines; D012436:S-Adenosylmethionine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000201:enzymology*
D003067:Coenzymes; D006160:Guanosine Triphosphate; D006867:Hydrolases; D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D000090006:Molybdenum Cofactors; D011621:Pteridines; D012436:S-Adenosylmethionine; C022261:molybdopterin; C511316:S-adenosylmethionine enzyme MoaA, Staphylococcus aureus