title: Structural and metabolic specificity of methylthiocoformycin for malarial adenosine deaminases.
abstract: Plasmodium falciparum is a purine auxotroph requiring hypoxanthine as a key metabolic precursor. Erythrocyte adenine nucleotides are the source of the purine precursors, making adenosine deaminase (ADA) a key enzyme in the pathway of hypoxanthine formation. Methylthioadenosine (MTA) is a substrate for most malarial ADAs, but not for human ADA. The catalytic site specificity of malarial ADAs permits methylthiocoformycin (MT-coformycin) to act as a Plasmodium-specific transition state analogue with low affinity for human ADA [Tyler, P. C., Taylor, E. A., Frohlich, R. G. G., and Schramm, V. L. (2007) J. Am. Chem. Soc. 129, 6872-6879]. The structural basis for MTA and MT-coformycin specificity in malarial ADAs is the subject of speculation [Larson, E. T., et al. (2008) J. Mol. Biol. 381, 975-988]. Here, the crystal structure of ADA from Plasmodium vivax (PvADA) in a complex with MT-coformycin reveals an unprecedented binding geometry for 5'-methylthioribosyl groups in the malarial ADAs. Compared to malarial ADA complexes with adenosine or deoxycoformycin, 5'-methylthioribosyl groups are rotated 130 degrees . A hydrogen bonding network between Asp172 and the 3'-hydroxyl of MT-coformycin is essential for recognition of the 5'-methylthioribosyl group. Water occupies the 5'-hydroxyl binding site when MT-coformycin is bound. Mutagenesis of Asp172 destroys the substrate specificity for MTA and MT-coformycin. Kinetic, mutagenic, and structural analyses of PvADA and kinetic analysis of five other Plasmodium ADAs establish the unique structural basis for its specificity for MTA and MT-coformycin. Plasmodium gallinaceum ADA does not use MTA as a substrate, is not inhibited by MT-coformycin, and is missing Asp172. Treatment of P. falciparum cultures with coformycin or MT-coformycin in the presence of MTA is effective in inhibiting parasite growth.
authors.affiliation: Department of Biochemistry, Albert Einstein College of Medicine, Yeshiva University, Bronx, New York 10461, USA.
authors.forename: Meng-Chiao
authors.initials: MC
authors.lastname: Ho
authors.forename: María B
authors.initials: MB
authors.lastname: Cassera
authors.forename: Dennis C
authors.initials: DC
authors.lastname: Madrid
authors.forename: Li-Min
authors.initials: LM
authors.lastname: Ting
authors.forename: Peter C
authors.initials: PC
authors.lastname: Tyler
authors.forename: Kami
authors.initials: K
authors.lastname: Kim
authors.forename: Steven C
authors.initials: SC
authors.lastname: Almo
authors.forename: Vern L
authors.initials: VL
authors.lastname: Schramm
mesh_terms: D000243:Adenosine Deaminase / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D000962:Antimalarials / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D003070:Coformycin / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D016778:Malaria, Falciparum / Q000201:enzymology* / Q000378:metabolism / Q000517:prevention & control; D010963:Plasmodium falciparum / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D000962:Antimalarials; D003070:Coformycin; D000243:Adenosine Deaminase