title: The crystal structure of thymidylate synthase from Pneumocystis carinii reveals a fungal insert important for drug design.
abstract: Thymidylate synthase from Pneumocystis carinii (PcTS) is an especially important drug target, since P. carinii is a fungus that causes opportunistic pneumonia infections in immune-compromised patients and is among the leading causes of death of AIDS patients. Thymidylate synthase (TS) is the sole enzyme responsible for the de novo production of deoxythymidine monophosphate and hence is crucial for DNA replication in every organism. Inhibitors selective for P. carinii TS over human TS would be greatly beneficial in combating this disease. The crystal structure of TS from P. carinii bound to its substrate, dUMP, and a cofactor mimic, CB3717, was determined to 2.6 A resolution. A comparison with other species of TS shows that the volume of the closed PcTS active-site is 20 % larger than that of five other TS closed active-sites. A two-residue proline insert that is strictly conserved among all fungal species of TS, and a novel C-terminal closing interaction involving a P. carinii-specific tyrosine residue are primarily responsible for this increase in volume. The structure suggests several options for designing an inhibitor specific to PcTS and avoiding interactions with human TS. Taking advantage of the residue substitutions of P. carinii TS over human TS enables the design of a selective inhibitor. Additionally, the larger volume of the active-site of PcTS is an important advantage for designing de novo inhibitors that will exclude the human TS active-site through steric hindrance.
authors.affiliation: Department of Biochemistry, University of California at San Francisco, San Francisco, CA, USA.
authors.forename: A C
authors.initials: AC
authors.lastname: Anderson
authors.forename: K M
authors.initials: KM
authors.lastname: Perry
authors.forename: D M
authors.initials: DM
authors.lastname: Freymann
authors.forename: R M
authors.initials: RM
authors.lastname: Stroud
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D003856:Deoxyuracil Nucleotides / Q000378:metabolism; D019281:Dimerization; D015195:Drug Design; D004791:Enzyme Inhibitors / Q000378:metabolism*; D005492:Folic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D011010:Pneumocystis / Q000201:enzymology*; D011485:Protein Binding; D011487:Protein Conformation; D011799:Quinazolines / Q000378:metabolism; D016415:Sequence Alignment; D013045:Species Specificity; D013379:Substrate Specificity; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism
chemical_list: D003856:Deoxyuracil Nucleotides; D004791:Enzyme Inhibitors; D011799:Quinazolines; C031662:CB 3717; D005492:Folic Acid; C007267:2'-deoxyuridylic acid; D013940:Thymidylate Synthase