N-glycosylation in piroplasmids: how sweet are tick-transmitted protozoa?

FLORIN-CHRISTENSEN M; RODRIGUEZ AE; SUAREZ CE; UETI MW; DELGADO F; IGNACIO E; SCHNITTGER L

Encuentro; 3rd International Babesiosis Meeting, Yale, USA; 2021

Introduction: N-glycosylation is the most frequent eukaryotic modifications of proteins and consists of the addition of an oligosaccharide of diverse composition and complexity to a surface-exposed asparagine residue of a protein generally destined to the secretory pathway. This study aimed at identifying the N-glycosylation pathways present in Babesia, Theileria and Cytauxzoon parasites, as well as exploring the potential biological significance of this process in B. bovis.Results: Analysis of eleven piroplasmid genomes revealed three distinct scenarios regarding N-glycosylation: Babesia sensu stricto (s.s.) species add one or two N-acetylglucosamine (NAcGlc) molecules to proteins; Theileria equi and Cytauxzoon felis add (NAcGlc)2-mannose, while B. microti and Theileria s.s. synthesize dolichol-P-P-NAcGlc and dolichol-P-P-(NAcGlc)2 without subsequent transfer to proteins. All piroplasmids possess the gene complement needed for the synthesis of the N-glycosylation substrates, dolichol-P and sugar nucleotides. The oligosaccharyl transferase of Babesia species, T. equi and C. felis, is predicted to be composed of only two subunits, STT3 and OST. Occurrence of short N-glycans in B. bovis merozoites was experimentally demonstrated by fluorescence microscopy using a NAcGlc-specific lectin. In vitro growth of B. bovis was significantly impaired by tunicamycin, an inhibitor of N-glycosylation, indicating a relevant role for Nglycosylation in this pathogen. Finally, genes coding for N-glycosylation enzymes and substrate biosynthesis aretranscribed in B. bovis blood and tick stages, suggesting that this pathway is biologically relevant throughout the parasite life cycle.Conclusion: Elucidation of the role/s exerted by N-glycans will increase our understanding of these successful tick-transmitted parasites, for which improved control measures are needed.