title: PurT-encoded glycinamide ribonucleotide transformylase. Accommodation of adenosine nucleotide analogs within the active site.
abstract: PurT-encoded glycinamide ribonucleotide transformylase, or PurT transformylase, functions in purine biosynthesis by catalyzing the formylation of glycinamide ribonucleotide through a catalytic mechanism requiring Mg(2+)ATP and formate. From previous x-ray diffraction analyses, it has been demonstrated that PurT transformylase from Escherichia coli belongs to the ATP-grasp superfamily of enzymes, which are characterized by three structural motifs referred to as the A-, B-, and C-domains. In all of the ATP-grasp enzymes studied to date, the adenosine nucleotide ligands are invariably wedged between the B- and C-domains, and in some cases, such as biotin carboxylase and carbamoyl phosphate synthetase, the B-domains move significantly upon nucleotide binding. Here we present a systematic and high-resolution structural investigation of PurT transformylase complexed with various adenosine nucleotides or nucleotide analogs including Mg(2+)ATP, Mg(2+)-5'-adenylylimidodiphosphate, Mg(2+)-beta,gamma-methyleneadenosine 5'-triphosphate, Mg(2+)ATPgammaS, or Mg(2+)ADP. Taken together, these studies indicate that the conformation of the so-called "T-loop," delineated by Lys-155 to Gln-165, is highly sensitive to the chemical identity of the nucleotide situated in the binding pocket. This sensitivity to nucleotide identity is in sharp contrast to that observed for the "P-loop"-containing enzymes, in which the conformation of the binding motif is virtually unchanged in the presence or absence of nucleotides.
authors.affiliation: Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: James B
authors.initials: JB
authors.lastname: Thoden
authors.forename: Steven M
authors.initials: SM
authors.lastname: Firestine
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Benkovic
authors.forename: Hazel M
authors.initials: HM
authors.lastname: Holden
mesh_terms: D000244:Adenosine Diphosphate / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000737:chemistry; D000266:Adenylyl Imidodiphosphate / Q000737:chemistry; D001665:Binding Sites; D003460:Crystallization; D018360:Crystallography, X-Ray; D019877:Hydroxymethyl and Formyl Transferases / Q000737:chemistry*; D051026:Phosphoribosylglycinamide Formyltransferase
chemical_list: D000266:Adenylyl Imidodiphosphate; C022571:adenosine 5'-O-(3-thiotriphosphate); D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D019877:Hydroxymethyl and Formyl Transferases; D051026:Phosphoribosylglycinamide Formyltransferase