Structural and metabolic specificity of methylthiocoformycin for malarial adenosine deaminases

Meng Chiao Ho, María B. Cassera, Dennis C. Madrid, Li Min Ting, Peter C. Tyler, Kami Kim, Steven C. Almo, Vern L. Schramm

Research output: Contribution to journalArticle

20 Scopus citations

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., Fröhlich, 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°. 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.

Original languageEnglish (US)
Pages (from-to)9618-9626
Number of pages9
JournalBiochemistry
Volume48
Issue number40
DOIs
StatePublished - 2009

ASJC Scopus subject areas

  • Biochemistry

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