title: Complexed structures of formylglycinamide ribonucleotide amidotransferase from Thermotoga maritima describe a novel ATP binding protein superfamily.
abstract: Formylglycinamide ribonucleotide amidotransferase (FGAR-AT) catalyzes the ATP-dependent synthesis of formylglycinamidine ribonucleotide (FGAM) from formylglycinamide ribonucleotide (FGAR) and glutamine in the fourth step of the purine biosynthetic pathway. FGAR-AT is encoded by the purL gene. Two types of PurL have been detected. The first type, found in eukaryotes and Gram-negative bacteria, consists of a single 140 kDa polypeptide chain and is designated large PurL (lgPurL). The second type, small PurL (smPurL), is found in archaea and Gram-positive bacteria and consists of an 80 kDa polypeptide chain. SmPurL requires two additional gene products, PurQ and PurS, for activity. PurL is a member of a protein superfamily that contains a novel ATP-binding domain. Structures of several members of this superfamily are available in the unliganded form. We determined five different structures of FGAR-AT from Thermotoga maritima in the presence of substrates, a substrate analogue, and a product. These complexes have allowed a detailed description of the novel ATP-binding motif. The availability of a ternary complex enabled mapping of the active site, thus identifying potential residues involved in catalysis. The complexes show a conformational change in the active site compared to the unliganded structure. Surprising discoveries, an ATP molecule in an auxiliary site of the protein and the conformational changes associated with its binding, provoke speculation about the regulatory role of the auxiliary site in formation of the PurLSQ complex as well as the evolutionary relationship of PurLs from different organisms.
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Mariya
authors.initials: M
authors.lastname: Morar
authors.forename: Ruchi
authors.initials: R
authors.lastname: Anand
authors.forename: Aaron A
authors.initials: AA
authors.lastname: Hoskins
authors.forename: JoAnne
authors.initials: J
authors.lastname: Stubbe
authors.forename: Steven E
authors.initials: SE
authors.lastname: Ealick
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry* / Q000378:metabolism; D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D019733:Carbon-Nitrogen Ligases with Glutamine as Amide-N-Donor / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D019143:Evolution, Molecular; D005973:Glutamine / Q000737:chemistry / Q000378:metabolism; D005998:Glycine / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012265:Ribonucleotides / Q000096:biosynthesis / Q000737:chemistry*; D040681:Structural Homology, Protein; D020124:Thermotoga maritima / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D012265:Ribonucleotides; D005973:Glutamine; C002824:phosphoribosyl-N-formylglycineamide; D000255:Adenosine Triphosphate; D019733:Carbon-Nitrogen Ligases with Glutamine as Amide-N-Donor; C022385:phosphoribosylformylglycinamidine synthetase; D005998:Glycine