Peculiarities of glycosylation of proteins in spores of microsporidia Paranosema (Antonospora) grylli

The long-term adaptation of microsporidia, a large group of fungi-related unicellular microorganisms, to intracellular parasitism has led to extreme minimization of the cell functional apparatus. For instance, diversity of carbohydrates in the composition of parasite glycoproteins and proteoglycans seems to be restricted to the presence of O-bound chains composed of mannose residues. This suggestion is based on the discovery in the genome of the human microsporidian Encephalitozoon cuniculi of three genes responsible for the O-mannosylation of proteins with a lack of enzymes participating in N-glycosylation. In the present work, peculiarities of protein glycosylation in spores of the microsporidian Paranosema grylli infecting the fat body of the Mediterranean field cricket Gryllus bimaculatus was studied. SDS-PAGE analysis of spore proteins with subsequent staining by periodate and Schiff reagent has shown that individual glycoproteins of P. grylli are highly glycosylated, while the maximal stain intensity was seen in the major polar-tube protein PTP1. Treatment of the extracted material with N-glycosidase F and hybridization with WGA lectin conjugated with horseradish peroxidase showed no presence of glycosylated proteins in the P. grylli spores. At the same time, the selectively extracted major protein of the exospore p40 was specifically recognized by lectin GNA conjugated with agarose balls. Pretreatment of p40 with α-and β-mannosidases decreased considerably the efficiency of binding. Since lectin GNA is specific towards mannose terminal residues, this indicates the O-mannosylation of the microsporidial exospore major protein. In spite of the intensive PTP1 glycosylation, extracted proteins of the P. grylli polar-tube had no specific binding with GNA-agarose, so the issue of peculiarities of their glycosylation remains an open question. Comparison of the obtained data with results of deciphering of the E. cuniuculi genome allows for the conclusion to be made that the minimization of the glycosylation apparatus of microsporidial proteins is the common peculiarity of this group of parasites.