FORMATION OF ENZYME COMPLEX BETWEEN OROTATE PHOSPHORIBOSYLTRANSFERASE AND OROTIDINE 5'-MONOPHOSPHATE DECARBOXYLASE OF PLASMODIUM FALCIPARUM

Abstract

Plasmodium falciparum, the causative agent of the most lethal form of human malaria, relies on de novo pyrimidime biosynthetic pathway. The parasite orotate phosphoribosyltransferase (OPRT) and orotidine 5'-monophosphate decarboxylase (OMPDC), the fifth and sixth enzyme of the pathway, is attractive target for antimalarial development. Previously, it was clearly established that the two enzymes in the malaria parasite exist physically as a heterotetrameric (OPRT)₂(OMPDC)₂ complex containing two subunits each of OPRT and OMPDC, and that the complex have catalytic kinetic advantages over the monofunctional enzyme. In this study, the protein-protein interaction in enzyme complex was identified using chemical cross-linker, liquid chromatography-mass spectrometric analysis and homology modeling. Interestingly, the unique insertions of low complexity region at the α2 and α5 helices of the parasite OMPDC, characterized by single amino acid repeat sequence which was not found in homologous proteins from other organisms, was located on the OPRT-OMPDC interface. The structural models for the protein-protein interaction of the heterotetrameric (OPRT)₂(OMPDC)₂ multienzyme complex were proposed. Based on the proteomic data and structural modeling, it is summarized that the low complexity region of human malaria parasite is responsible for the OPRT-OMPDC interaction. The structural complex of the parasite enzymes, thus, represents an efficient functional kinetic advantage.