Glycosylphosphatidylinositol metabolism is critical for the survival of bovine Babesia parasites

RODRIGUEZ AE; TORRA F; ECHAIDE I; SCHNITTGER L; FLORIN-CHRISTENSEN M

Conferencia; ApiCOWplexa 2013: 2nd International Meeting on Apicomplexan Parasites in Farm Animals; 2013

Glycosylphosphatidylinositols (GPIs), formed by an inositol phospholipid attached to a chain of typically three mannose molecules, are abundantly present in several protozoan parasites, and participate in host-pathogen interactions, both as modulators of host immune responses, and as key molecules in the parasitic life cycle. We have focused on the GPI metabolism of Babesia bovis and B. bigemina, the main causative agents of bovine babesiosis, in the search for new therapeutic targets. In silico we identified the genes responsible for the GPI metabolic pathway in the fully annotated genome of B. bovis, by BLAST searches using the corresponding sequences of related eukaryotes. In the case of the non-annotated genome of B. bigemina, in silico search in genomic contigs revealed the DNA segments containing the genes of interest which were PCR-amplified and sequenced. Both parasites, B. bovis and B. bigemina contain eight enzymes (PIG-A, GPI-1, PIG-L, PIG-W, DPM-1, PIG-M, PIG-V, PIG-O) that are involved in the synthesis of GPIs in the endoplasmic reticulum, starting from phosphatidylinositol, N-acetylglucosamine, dolichol-phosphate and mannose-GDP. The corresponding enzymatic steps are common to the production of free GPIs and GPI protein anchors. Subsequently, GPI-8, and GAA-1 catalyze the attachment of the GPI anchor to a nascent protein. RT-PCR studies performed on three of the identified genes showed that they are transcribed in pathogenic and attenuated strains of B. bovis and B. bigemina. Noteworthy, mannosamine, a competitive inhibitor of GPI synthesis, hampered in vitro growth of merozoites of both parasites, in a dose-dependent manner. These results are consistent with a critical role for GPI-anchored proteins in the attachment to and/or invasion of erythrocytes, a critical event in Babesia sp. life cycle. In addition, they could be indicative for an essential role of free GPIs in this process. Financed by the European Commission (INCO 245145 PIROVAC), MINCyT, Argentina (PICT2010-0438 and PICT2011-0114) and INTA, Argentina (PE 1131034)