The putative chitin deacetylase ofEncephalitozoon cuniculi: A surface protein implicated in microsporidian spore-wall formation

Abstract

Microsporidia are fungal-like unicellular eukaryotes which develop as obligate intracellular parasites. They differentiate into resistant spores that are protected by a thick cell wall composed of glycoproteins and chitin. Despite an extensive description of the fibrillar structure of this wall, very little is known about its protein components and deposit mechanisms. In this study on the human pathogen Encephalitozoon cuniculi, we identify by mass spectrometry the target of polyclonal antibodies previously raised against a 33-kDa protein located at the outer face of the parasite plasma membrane. This 254-amino acid protein is encoded by the ECU11_0510 open reading frame and presents two isoforms of 33 and 55 kDa. Sequence analysis supports an assignment to the polysaccharide deacetylase family with a suspected chitin deacetylase activity (EcCDA). As demonstrated by TEM studies, EcCDA is present at the plasma membrane of the early stages of E. cuniculi life-cycle. At the sporoblast stage, the enzyme accumulates especially in paramural bodies which are convolutions of the plasma membrane opened to the wall. The identification of an EcCDA homologue in the insect parasite Antonospora locustae (ex Nosema locustae) suggests a widespread distribution of this enzyme among Microsporidia. This characterization of a new microsporidian surface protein creates new perspectives to understand spore wall formation and spore resistance.

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.…”

“…Although chitin is the major component of the spore wall, only one chitin-associated protein has been identified. The chitin deacetylase activity of E. cuniculi (EcCDA) has been confirmed to be expressed during sporogonic stages (14). Currently, the deproteinated chitin spore coats (DCSCs) of the N. bombycis endospore are isolated using a heated alkali solution (15).…”

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).…”

Branching Network of Proteinaceous Filaments within the Parasitophorous Vacuole of Encephalitozoon cuniculi and Encephalitozoon hellem

“…EnP1 was later localized to the exospore as well and found to mediate adherence to host cells (36). Similar techniques were used to localize a putative chitin deacetylase to the E. cuniculi plasma membrane-endospore interface, suggesting a role in microsporidian endospore development (6).…”