Secretion of Antonospora (Paranosema) locustae Proteins into Infected Cells Suggests an Active Role of Microsporidia in the Control of Host Programs and Metabolic Processes

Abstract

Molecular tools of the intracellular protozoan pathogens Apicomplexa and Kinetoplastida for manipulation of host cell machinery have been the focus of investigation for approximately two decades. Microsporidia, fungi-related microorganisms forming another large group of obligate intracellular parasites, are characterized by development in direct contact with host cytoplasm (the majority of species), strong minimization of cell machinery, and acquisition of unique transporters to exploit host metabolic system. All the aforementioned features are suggestive of the ability of microsporidia to modify host metabolic and regulatory pathways. Seven proteins of the microsporidium Antonospora (Paranosema) locustae with predicted signal peptides but without transmembrane domains were overexpressed in Escherichia coli. Western-blot analysis with antibodies against recombinant products showed secretion of parasite proteins from different functional categories into the infected host cell. Secretion of parasite hexokinase and α/β-hydrolase was confirmed by immunofluorescence microscopy. In addition, this method showed specific accumulation of A. locustae hexokinase in host nuclei. Expression of hexokinase, trehalase, and two leucine-rich repeat proteins without any exogenous signal peptide led to their secretion in the yeast Pichia pastoris. In contrast, α/β-hydrolase was not found in the culture medium, though a significant amount of this enzyme accumulated in the yeast membrane fraction. These results suggest that microsporidia possess a broad set of enzymes and regulatory proteins secreted into infected cells to control host metabolic processes and molecular programs.

The invasive cell coat at the microsporidian Trachipleistophora hominis–host cell interface contains secreted hexokinases

“…The widespread expression of secreted HKs in the face of genome compaction suggests an essential role. So far, two studies have localized signal peptide‐containing microsporidian HKs to host cell compartments ((Senderskiy et al., ), A. locustae , nucleus; (Reinke et al., ) N. parisii, cytoplasm) although they did not establish functions for HKs at these sites.…”

Transcriptome sequencing and characterization of ungerminated and germinated spores of <italic>Nosema bombycis</italic>

“…Some microsporidian spores could utilize glycosaminoglycans (GAGs) as host cell receptors for adhesion and infection, possibly through the interaction with a major SWP named EnP1 [58]. In Antonospora (Paranosema) locustae, fat bodies from experimentally infected and controlled Locusta migratoria locusts were not decorated with anti-ricin B antibodies as revealed by immunoblotting [59]. Based on these findings, we infer that the gene expression level of NbRBL might be high in dormant state to accumulate NbRBL protein, and that this functional protein might play a role in spore invasion after germination.…”

Microsporidia–host interactions

“…This secretion sequence was shown to be functional in a heterologous yeast expression system, where it could direct traffic through the yeast secretory system, supporting a model where microsporidia hexokinase could be directed into the host cell and perhaps promote anabolic metabolism in vivo [19]. Hexokinase secretion was recently verified experimentally using antibodies directed against hexokinase of Antonospora locustae , a species of microsporidia that infects locusts [20]. Interestingly, hexokinase localized to the nucleus in these studies, suggesting that it could alter host gene expression.…”