Complexed structures of formylglycinamide ribonucleotide amidotransferase from Thermotoga maritima describe a novel ATP binding protein superfamily.
Publication Type:Journal Article
Source:Biochemistry, Volume 45, Issue 50, p.14880-95 (2006)
Keywords:Adenosine Triphosphate, Amino Acid Motifs, Bacterial Proteins, Binding Sites, Carbon-Nitrogen Ligases with Glutamine as Amide-N-Donor, Crystallography, X-Ray, Evolution, Molecular, Glutamine, Glycine, Protein Binding, Protein Structure, Tertiary, Ribonucleotides, Structural Homology, Protein, Thermotoga maritima
<p>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.</p>