Assessment and comparison of the Babesia bovis and Theileria annulata GPI-anchored proteome by bioinformatics

RODRIGUEZ AE, FLORIN-CHRISTENSEN M, SCHNITTGER L

Congreso; VI International Conference on Ticks and Tick-borne Pathogens; 2008

Assessment and comparison of the Babesia bovis and Theileria annulata GPI-anchored proteome by bioinformatics Rodríguez, A.E., Florin-Christensen M, and *Schnittger L Institute of Pathobiology, CICVyA, Castelar; and 2EEA-Rafaela, INTA, Argentina; e-mail: lschnittger@cnia.inta.gov.ar  The tick-transmitted hemoprotozoan piroplasmids Babesia bovis and Theileria annulata are the causative agents of bovine babesiosis and tropical theileriosis, respectively, in vast tropical and subtropical regions. Efforts are made to identify suitable vaccine candidates for the development of safer and more efficient vaccines against these diseases. In B. bovis and T. annulata the variable merozoite surface antigen (VMSA) and the major merozoite piroplasm surface antigen (mMPSA) family, respectively, are considered as subunit vaccine candidates as they are likely to participate in erythrocyte invasion. VMSAs and mMPSAs belong to a group of surface proteins that are anchored to the plasma membrane via a carboxy-terminal glycosylphosphatidylinositol (GPI) modification. In order to identify additional GPI-anchored proteins that may represent vaccine candidates the conceptually translated proteome of B. bovis was screened with a series of bioinformatic tools (GPI-SOM, GPIPE, and Big-PI) that are predictive for GPI-anchor attachment. Altogether, 84 proteins were prognosticated of which 59 could be excluded based on the following rejection criteria: i) absence of an N terminal signal peptide (SignalP 3.0), ii) absence of a C terminal transmembrane (TM) region (DAS), or iii) prediction of being a non-TM protein (DAS). The remaining 25 include the five VMSA members while all others are annotated as hypothetical proteins of unknown function that await experimental identification. Concerning T. annulata, a similar strategy resulted in a preliminary list of 136 forecast GPI-anchored proteins of which, after applying the outlined rejection criteria, 42 could be confidently shortlisted. These include the merozoite-piroplasm surface protein (Tams), a member of the mMPSA family, and the sporozoite surface protein (TaSP), while the function of the remaining proteins is hypothetical or unknown. Noteworthy, 8 out of 25 and 20 out of 42 shortlisted GPI-anchored proteins of B. bovis and T. annulata, respectively, are predicted to own 3 or more TM regions. Currently, this condition is considered rare in GPI-anchored proteins. Future experimental investigation will show the predictive validity of this fraction of GPI-anchored candidate proteins. Our analysis further suggests that the GPI-anchored proportion of the B. bovis proteome is somewhat lower than that of T. annulata which is in agreement with the existence of an additional parasite stage in the latter parasite. Exploration of the presented shortlist is worthwhile as it contains predominantly unknown proteins and allows a focused and systematic experimental approach to reveal further GPI-anchored proteins of both parasites for inclusion in future vaccination trials. Supported by INCO 003691-MEDLABAB; and PIP 5580, CONICET, Argentina. AER received a Doctoral Fellowship from CONICET and AC and MFC are CONICET Researchers