Background. S-adenosylmethionine decarboxylase (AdoMetDC) is required for the biosynthesis of the polyamine spermidine, needed for cell growth in all organisms. In trypanosomes spermidine is conjugated with glutathione to form a unique metabolite known as trypanothione that functions in cellular redox reactions (1). Inhibitors of polyamine biosynthesis have been widely studied as anti-proliferative agents (2, 3). The most successful clinical application of these inhibitors is the treatment of African sleeping sickness with the ornithine decarboxylase suicide inhibitor a-difluoromethylornithine (eflornithine) (4). Eflornithine is the only therapy for sleeping sickness with a known mechanism of action, and its effectiveness demonstrates the importance of the polyamine pathway to the parasite. T. brucei AdoMetDC is activated by formation of a heterodimer with a catalytically inactive regulatory subunit termed prozyme that arose in the trypanosomatids as a gene duplication of the ancestral enzyme (5). A prozyme homolog is also found in Leishmania and T. cruzi, but not in any species outside of the kinetoplatida lineage. Thus the regulation of AdoMetDC by an inactive homolog is unique to the trypanosomatid parasites. The finding has implications for both the regulation of polyamines in the parasite, and for the development of enzyme inhibitors that will block this essential pathway. An essential and druggable target. Knockout of the AdoMetDC gene in the trypanosomatid Leishmania donovani causes spermidine auxotropy (6). Unpublished data from my lab (Phillips, MA) also demonstrates that knockdown of AdoMetDC by RNAi in blood form T. brucei results in cell growth arrest followed by cell death. A suicide inhibitor of AdoMetDC, MDL73811, is able to cure infections of T. brucei in rodents (7) and it has activity against Trypanosoma cruzi (8). Thus, AdoMetDC has been validated both genetically and chemically to be an essential enzyme. Structure and Assay. AdoMetDC is a pyruvoyl-dependent enzyme. The X-ray structures of the human, plant and bacterial enzymes have been reported (9, 10). The trypansomatid enzymes can be easily expressed to high levels in bacteria, however the current enzyme assay is based on trapping of 14CO2 and thus is not suitable for HTS analysis. 1. A. Fairlamb, P. Blackburn, B. Chait, A. Cerami, Science 227, 1485 (1985). 2. E. W. Gerner, F. L. Meyskens, Jr., Nat Rev Cancer 4, 781 (Oct, 2004). 3. L. Marton, A. Pegg, Annu. Rev. Pharmacol. Toxicol. 35, 55 (1995). 4. C. Bacchi, H. Nathan, S. Hunter, Science 210, 332 (1980). 5. E. K. Willert, R. Fitzpatrick, M. A. Phillips, Proc Natl Acad Sci U S A 104, 8275 (2007). 6. S. Roberts et al., J. Biol. Chem. 277, 5902 (2002). 7. C. Bacchi et al., Antimicrobial agents and Chemotherapy 36, 2736 (1992). 8. M. Yakubu, S. Majumder, F. Kierszenbaum, J. Parasitol. 79, 525 (1993). 9. J. Ekstrom, W. Tolbert, H. Xiong, A. Pegg, S. Ealick, Biochemistry 40, 9495 (2001). 10. W. Tolbert et al., Biochemistry 42, 2386 (2003). Target ID: geneDB number = Tb927.6.4410, Tb927.6.4460 EC number (if enzyme) = EC 188.8.131.52 target name = S-adenosylmethionine decarboxylase AdoMetDC regulatory protein, termed prozyme geneDB number =Tb927.6.4470; required for full activity Assay: No convenient assay at present Availability: Can be expressed > 1 mg/L in soluble, active form Activity: Significant (= 1 full time person)
Target ID: geneDB number = Tb927.6.4410, Tb927.6.4460 EC number (if enzyme) = EC 184.108.40.206 target name = S-aden
Validation: Genetic AND chemical evidence
Assay status: No convenient assay at present
Availability: Can be expressed > 1 mg/L in soluble, active form
Activity: Significant (>= 1 full time person)
Structure of a human S-adenosylmethionine decarboxylase self-processing ester intermediate and mechanism of putrescine stimulation of processing as revealed by the H243A mutant. (2001).
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Inhibition of S-adenosyl-L-methionine (AdoMet) decarboxylase by the decarboxylated AdoMet analog 5'-([(Z)-4-amino-2-butenyl]methylamino)-5'-deoxyadenosine (MDL 73811) decreases the capacities of Trypanosoma cruzi to infect and multiply within a mammalian host cell. (1993).
J Parasitol 79: