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Structures of apo and complexed Escherichia coli glycinamide ribonucleotide transformylase.

ABSTRACT: The three-dimensional structure of phosphoribosylglycinamide formyltransferase (10-formyltetrahydrofolate:5'-phosphoribosylglycinamide formyltransferase, EC 2.1.2.2) has been solved both as an apoenzyme at 2.8-A resolution and as a ternary complex with the substrate glycinamide ribonucleotide and a folate inhibitor at 2.5-A resolution. The structure is a modified doubly wound alpha/beta sheet with flexibility in the active site, including a disordered loop in the apo structure, which is ordered in the ternary complex structure. This enzyme is a target for anti-cancer therapy and now for structure-based drug design.

SUBMITTER: Almassy RJ

PROVIDER: S-EPMC49448 | biostudies-other | 1992 Jul

REPOSITORIES: biostudies-other

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Structures of apo and complexed Escherichia coli glycinamide ribonucleotide transformylase.

Almassy R J RJ Janson C A CA Kan C C CC Hostomska Z Z

Proceedings of the National Academy of Sciences of the United States of America 19920701 13

The three-dimensional structure of phosphoribosylglycinamide formyltransferase (10-formyltetrahydrofolate:5'-phosphoribosylglycinamide formyltransferase, EC 2.1.2.2) has been solved both as an apoenzyme at 2.8-A resolution and as a ternary complex with the substrate glycinamide ribonucleotide and a folate inhibitor at 2.5-A resolution. The structure is a modified doubly wound alpha/beta sheet with flexibility in the active site, including a disordered loop in the apo structure, which is ordered ...[more]

PMID: 1631098

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Project description:Low fidelity Escherichia coli DNA polymerase V (pol V/UmuD'2C) is best characterized for its ability to perform translesion synthesis (TLS). However, in recA730 lexA(Def) strains, the enzyme is expressed under optimal conditions allowing it to compete with the cell's replicase for access to undamaged chromosomal DNA and leads to a substantial increase in spontaneous mutagenesis. We have recently shown that a Y11A substitution in the "steric gate" residue of UmuC reduces both base and sugar selectivity of pol V, but instead of generating an increased number of spontaneous mutations, strains expressing umuC_Y11A are poorly mutable in vivo. This phenotype is attributed to efficient RNase HII-initiated repair of the misincorporated ribonucleotides that concomitantly removes adjacent misincorporated deoxyribonucleotides. We have utilized the ability of the pol V steric gate mutant to promote incorporation of large numbers of errant ribonucleotides into the E. coli genome to investigate the fundamental mechanisms underlying ribonucleotide excision repair (RER). Here, we demonstrate that RER is normally facilitated by DNA polymerase I (pol I) via classical "nick translation". In vitro, pol I displaces 1-3 nucleotides of the RNA/DNA hybrid and through its 5'→3' (exo/endo) nuclease activity releases ribo- and deoxyribonucleotides from DNA. In vivo, umuC_Y11A-dependent mutagenesis changes significantly in polymerase-deficient, or proofreading-deficient polA strains, indicating a pivotal role for pol I in ribonucleotide excision repair (RER). However, there is also considerable redundancy in the RER pathway in E. coli. Pol I's strand displacement and FLAP-exo/endonuclease activities can be facilitated by alternate enzymes, while the DNA polymerization step can be assumed by high-fidelity pol III. We conclude that RNase HII and pol I normally act to minimize the genomic instability that is generated through errant ribonucleotide incorporation, but that the "nick-translation" activities encoded by the single pol I polypeptide can be undertaken by a variety of back-up enzymes.

Project description:BackgroundThe enzyme dihydropteroate synthase (DHPS) participates in the de novo synthesis of folate cofactors by catalyzing the formation of 7,8-dihydropteroate from condensation of p-aminobenzoic acid with 6-hydroxymethyl-7,8-dihydropteroate pyrophosphate. DHPS is absent from humans, who acquire folates from diet, and has been validated as an antimicrobial therapeutic target by chemical and genetic means. The bacterium Burkholderia cenocepacia is an opportunistic pathogen and an infective agent of cystic fibrosis patients. The organism is highly resistant to antibiotics and there is a recognized need for the identification of new drugs against Burkholderia and related Gram-negative pathogens. Our characterization of the DHPS active site and interactions with the enzyme product are designed to underpin early stage drug discovery.ResultsAn efficient recombinant protein expression system for DHPS from B. cenocepacia (BcDHPS) was prepared, the dimeric enzyme purified in high yield and crystallized. The structure of the apo-enzyme and the complex with the product 7,8-dihydropteroate have been determined to 2.35 Å and 1.95 Å resolution respectively in distinct orthorhombic crystal forms. The latter represents the first crystal structure of the DHPS-pterin product complex, reveals key interactions involved in ligand binding, and reinforces data generated by other structural studies. Comparisons with orthologues identify plasticity near the substrate-binding pocket and in particular a range of loop conformations that contribute to the architecture of the DHPS active site. These structural data provide a foundation for hit discovery. An intriguing observation, an artifact of the analysis, that of a potential sulfenamide bond within the ligand complex structure is mentioned.ConclusionStructural similarities between BcDHPS and orthologues from other Gram-negative species are evident as expected on the basis of a high level of sequence identity. The presence of 7,8-dihydropteroate in the binding site provides details about ligand recognition by the enzyme and the different states of the enzyme allow us to visualize distinct conformational states of loops adjacent to the active site. Improved drugs to combat infections by Burkholderia sp. and related Gram-negative bacteria are sought and our study now provides templates to assist that process and allow us to discuss new ways of inhibiting DHPS.

Dataset Information

Structures of apo and complexed Escherichia coli glycinamide ribonucleotide transformylase.

Publications

Structures of apo and complexed Escherichia coli glycinamide ribonucleotide transformylase.

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