title: Non-canonical active site architecture of the radical SAM thiamin pyrimidine synthase.
abstract: Radical S-adenosylmethionine (SAM) enzymes use a [4Fe-4S] cluster to generate a 5'-deoxyadenosyl radical. Canonical radical SAM enzymes are characterized by a β-barrel-like fold and SAM anchors to the differentiated iron of the cluster, which is located near the amino terminus and within the β-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.
authors: Department of Chemistry and Chemical Biology, Cornell University, 120 Baker Lab, Ithaca, New York 14853, USA.
authors: Michael K
authors: MK
authors: Fenwick
authors: Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA.
authors: Angad P
authors: AP
authors: Mehta
authors: Department of Chemistry and Chemical Biology, Cornell University, 120 Baker Lab, Ithaca, New York 14853, USA.
authors: Yang
authors: Y
authors: Zhang
authors: Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA.
authors: Sameh H
authors: SH
authors: Abdelwahed
authors: Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA.
authors: Tadhg P
authors: TP
authors: Begley
authors: Department of Chemistry and Chemical Biology, Cornell University, 120 Baker Lab, Ithaca, New York 14853, USA.
authors: Steven E
authors: SE
authors: Ealick
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D002384:Catalysis; D020134:Catalytic Domain; D003038:Cobamides / Q000378:metabolism*; D018360:Crystallography, X-Ray; D019751:Intramolecular Transferases / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011743:Pyrimidines / Q000096:biosynthesis*; D012436:S-Adenosylmethionine / Q000378:metabolism*; D013831:Thiamine / Q000096:biosynthesis*
chemical_list: D001426:Bacterial Proteins; D003038:Cobamides; D007506:Iron-Sulfur Proteins; D011743:Pyrimidines; C105797:ThiC protein, Bacteria; D012436:S-Adenosylmethionine; D019751:Intramolecular Transferases; C021570:methylaspartate mutase; C000913:cobamamide; C030986:pyrimidine; D013831:Thiamine