National Center for
4S26: Crystal Structure Of Arabidopsis Thaliana Thic With Bound Imidazole Ribonucleotide, S-adenosylhomocysteine, Fe4s4 Cluster And Zn (monoclinic Crystal Form)
Nat Commun (2015) 6 p.6480
Radical S-adenosylmethionine (SAM) enzymes use a [4Fe-4S] cluster to generate a 5'-deoxyadenosyl radical. Canonical radical SAM enzymes are characterized by a beta-barrel-like fold and SAM anchors to the differentiated iron of the cluster, which is located near the amino terminus and within the beta-barrel, through its amino and carboxylate groups. Here we show that ThiC, the thiamin pyrimidine synthase in plants and bacteria, contains a tethered cluster-binding domain at its carboxy terminus that moves in and out of the active site during catalysis. In contrast to canonical radical SAM enzymes, we predict that SAM anchors to an additional active site metal through its amino and carboxylate groups. Superimposition of the catalytic domains of ThiC and glutamate mutase shows that these two enzymes share similar active site architectures, thus providing strong evidence for an evolutionary link between the radical SAM and adenosylcobalamin-dependent enzyme superfamilies.