Developmental Expression of Two Spore Wall Proteins during Maturation of the Microsporidian Encephalitozoon intestinalis

Abstract

Microsporidia are intracellular eukaryotes that infect many animals and cause opportunistic infections in AIDS patients. The disease is transmitted via environmentally resistant spores. Two spore wall constituents from the microsporidian Encephalitozoon intestinalis were characterized. Spore wall protein 1 (SWP1), a 50-kDa glycoprotein recognized by monoclonal antibody (MAb) 11B2, was detected in developing sporonts and at low levels on the surfaces of mature spores. In contrast, SWP2, a 150-kDa glycoprotein recognized by MAb 7G7, was detected on fully formed sporonts and was more abundant on mature spores than SWP1. Nevertheless, the SWPs appeared to be complexed on the surfaces of mature spores. SWP1 and SWP2 are similar at the DNA and protein levels and have 10 conserved cysteines in the N-terminal domain, suggesting similar secondary structures. The C-terminal domain of SWP2 has a unique region containing 50 repeating 12-or 15-amino-acid units that lacks homology to known protein motifs. Antibodies from mice infected with E. intestinalis recognized SWP1 and SWP2. The characterization of two immunogenic SWPs from E. intestinalis will allow the study of exospore structure and function and may lead to the development of useful tools in the diagnosis and treatment of microsporidiosis.Microsporidia are obligate intracellular organisms that infect a wide variety of animals ranging from insects and fish to mammals, including humans. Of over 1,000 microsporidial species identified, at least 13 are known to infect humans (10). The species more commonly identified in humans are members of the families Enchephalitozoonidae and Enterocytozoonidae. In humans, microsporidiosis is found mostly in human immunodeficiency virus-infected and AIDS patients and commonly results in severe diarrhea and wasting (3,20). However, microsporidiosis also occurs in immunocompetent individuals and common farm animals (21,29,32).Microsporidia infect cells by a unique mechanism (reviewed in reference 31). Upon close association of a spore with a suitable host cell, a hollow polar filament is extruded from the spore into the host cell's cytoplasm. The infectious sporoplasm passes through the polar filament into the cell, initiating infection (18). Alternatively, the spore may be internalized by phagocytosis (33). The microsporidia then enter a stage of proliferative growth by nuclear fission called merogony, resulting in large and less structurally defined cells. In the family Encephalitozoonidae, the transition from meront to the next stage (sporont) is marked by aggregation of electron-dense material on the outer spore membrane. These immature cells are localized to the edge of the parasitophorous vacuole (PV). Then, in most cases, fully formed sporonts break away from the edge of the PV to reside internally (7, 12). Sporonts undergo continuous transition into sporoblasts, after which organelles organize and become more defined. At this stage, the cells form an electron-lucent material, the endospore, immediately inside the exospore region...

The microsporidian polar tube: A highly specialised invasion organelle

“…In addition, several monoclonal antibodies were reported to recognise spore wall antigens (Visvesvara et al, 1994;Beckers et al, 1996;Lujan et al, 1998). A glycine-and serine-rich 51-kDa protein named SWP1 is localised to the exospore in E. cuniculi (Bohne et al, 2000) and E. intestinalis (Hayman et al, 2001). The corresponding gene, swp1, has been identified in E. cuniculi (Bohne et al, 2000), E. hellem (Bohne et al, 2000) and E. intestinalis (Hayman et al, 2001).…”

“…A glycine-and serine-rich 51-kDa protein named SWP1 is localised to the exospore in E. cuniculi (Bohne et al, 2000) and E. intestinalis (Hayman et al, 2001). The corresponding gene, swp1, has been identified in E. cuniculi (Bohne et al, 2000), E. hellem (Bohne et al, 2000) and E. intestinalis (Hayman et al, 2001). SWP1 is absent in meronts and first seen in early sporonts at a time when organisms translocate from the periphery to the centre of the parasitophorous vacuole (Bohne et al, 2000).…”

Interaction and Assembly of Two Novel Proteins in the Spore Wall of the Microsporidian Species Nosema bombycis and Their Roles in Adherence to and Infection of Host Cells

“…However, few studies have reported on the interactions between spore wall proteins (SWPs) and the DCSCs in microsporidia. At present, several spore wall proteins that are localized to the exospore or endospore have been identified in the genus Encephalitozoonidae (14,(16)(17)(18)(19)(20). For N. bombycis, only two exosporal proteins (21-23), three endosporal proteins (21,24,25), and a BAR-2 spore wall protein (26) have been characterized.…”

Expression and characterization of a novel spore wall protein from Nosema bombycis

“…However, little is currently known about the components of the spore wall. Only seven spore wall proteins in E. cuniculi and E. intestinalis were identified by monoclonal or polyclonal antibodies (Bohne et al, 2000;Brosson et al, 2005;Peuvel-Fanget et al, 2006;Southern et al, 2007;Xu et al, 2006;Hayman et al, 2001). Among fourteen hypothetical spore wall proteins from N. Bombycis deposited in GenBank data, only five complete spore wall proteins have been identified, which contain two endosporal proteins(SWP25 and SWP30) and three exosporal proteins (NbSWP5, SWP26, and SWP32) (Wu et al, 2008;Wu et al, 2009;Li et al, 2009;Cai et al, 2011).…”

“…To date, only a total of seven spore wall proteins have been reported in E. cuniculi (Bohne et al, 2000;Brosson et al, 2005;Peuvel-Fanget et al, 2006;Southern et al, 2007;Xu et al, 2006) and Encephalitozoon intestinalis (Southern et al, 2007;Hayman et al, 2001), and four spore wall proteins from N. bombycis including SWP25, SWP30, SWP26 and SWP32 were addressed on the location and function (Wu et al, 2008;Li et al, 2009). In our previous study, we identified an exosporal protein NbSWP5 that can protect spores from phagocytic uptaking by cultured insect cells (Cai et al, 2011).…”