Protein glycosylation in the spores of the microsporidia Paranosema (Antonospora) grylli
Long adaptation of microsporidia, a large group of fungi-related protozoa, to intracellular lifestyle has resulted in drastic minimization of a parasite cell. Thus, diversity of carbohydrates in microsporidia glycoproteins and proteoglycans is expected to be restricted by O-linked manno-oligosaccharides because three genes involved in O-mannosylation of proteins and no components of N-linked glycosylation machinery were found in genome of human pathogen Encephalitozoon cuniculi. In this study we investigated glycosylation of spore proteins of microsporidia Paranosema (Antonospora) grylli infecting crickets Gryllus bimaculatus. Using periodic acid-Shiff reagent staining we have demonstrated that some P. grylli spore proteins are highly-glycosylated. The major polar tube protein (PTP1) of 56 kDa was shown as the most intensively decorated band. The experiments with N-glycosidase F and WGA lectin did not reveal any N-glycosylated proteins in P. grylli spores. At the same time, incubation of major spore wall protein of 40 kDa (p40) with mannose specific lectin GNA resulted in specific binding that was reduced by pretreatment of the protein with mannosidases. Interestingly, in spite of PTP1 glycosylation, polar tube proteins extracted from P. grylli spores were not precipitated by GNA-agarose. Since P. grylli and E. cuniculi are distantly related, our data suggest that dramatic reduction of protein glycosylation machinery is a common feature of microsporidia.
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ABSTRACT: To infect their host cells the Microsporidia use a unique invasion organelle, the polar tube complex. During infection, the organism is injected into the host cell through the hollow polar tube formed during spore germination. Currently, three proteins, PTP1, PTP2, and PTP3 have been identified by immunological and molecular techniques as being components of this structure. Genomic data suggests that Microsporidia are capable of O-linked, but not N-linked glycosylation as a post-translational protein modification. Cells were infected with Encephalitozoon cunicuili, labeled with radioactive mannose or glucosamine, and the polar tube proteins were examined for glycosylation. PTP1 was clearly demonstrated to be mannosylated consistent with 0-glycosylation. In addition, it was evident that several other proteins were mannosylated, but no labeling was seen with glucosamine. The observed post-translational mannosylation of PTP1 may be involved in the functional properties of the polar tube, including its adherence to host cells during penetration.
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ABSTRACT: All of the members of the microsporidia possess a unique, highly specialized invasion mechanism that involves the polar tube and spore wall. This chapter reviews the data on the organization, structure, and function of this invasion organelle. The application of immunological and molecular techniques and recent genome sequencing data has resulted in the identification of multiple polar tube and spore wall proteins (SWPs). The interactions of these identified proteins in the formation and function of the polar tube and spore wall remain to be determined. Inside the spore, the polar tube is filled with material and is often termed the polar filament; however, this chapter uses the term polar tube to refer to this structure when it is within the spore as well as when it forms a hollow tube after germination and is found outside the spore. The chapter presents details on the spore activation and discharge.
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