ENZYMES OF POLYAMINE METABOLISM

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Polyamines, including putrescine, spermidine, and spermine, are essential for normal cell growth in both prokaryotic and eukaryotic cells. The second rate-limiting step in polyamine biosynthesis is catalyzed by S-adenosylmethionine decarboxylase (AdoMetDC). In this reaction, S-adenosylmethionine (AdoMet) is decarboxylated to form S-adenosylmethioninamine (dcAdoMet). AdoMetDC is at a key branch point in the pathway as AdoMet can be used as a substrate for the methylation of DNA, proteins, and phospholipids, while dcAdoMet is committed to polyamine biosynthesis. We solved the structure of Thermotoga maritima, human, and potato AdoMetDC as well as complexes of the human enzyme with a number of inhibitors. Recent biochemical work has characterized AdoMetDC from the trypanosomatid parasites, Trypanosoma brucei (T. brucei) and Trypanosoma cruzi (T. cruzi), which cause disease and deaths for millions, particularly within developing countries. T. brucei causes the West African form of sleeping sickness and T. cruzi causes Chagas disease. Current therapies for treating both of these diseases are limited, and many of the drugs are highly toxic. In animal models, the AdoMetDC inhibitor MDL73811 was effective in inhibiting infection by both T. cruzi and T. brucei; thus, AdoMetDC is a promising, viable drug target for combating these trypanosomatid parasites. It is known from biochemical studies that the catalytic activity of the trypanosomatid AdoSAMDCs are enhanced by the formation of a heterodimer with a catalytically inactive regulatory subunit, termed the prozyme. Formation of a heterodimer stimulates T. brucei AdoMetDC activity 1000-fold, while the T. cruzi prozyme increases the catalytic rate constant almost 500-fold. However, the mechanism underlying this activation by the prozyme remains unknown. We are working on solving the individual structure of the T. brucei and T. cruzi AdoMet, prozyme, as well as the enzyme complex.