Microsporidia are obligate intracellular parasites, and a derivative of fungi, which harbor a rigid spore wall to resist adverse environmental pressures. The spore wall
protein, which is thought to be the first and direct
protein interacting with the host cell, may play a key role in the process of
microsporidia infection. In this study, we report a
protein, NbHSWP11, with a dnaJ domain. The
protein also has 6
heparin-binding motifs which are known to interact with extracellular
glycosaminoglycans. Syntenic analysis indicated that gene loci of Nbhswp11 are conserved and syntenic between Nosema bombycis and Nosema ceranae. Phylogenetic tree analysis showed that Nbhswp11 clusters with fungal
dnaJ proteins and has 98% identity with an N. bombycis
dnaJ protein. Nbhswp11 was transcribed throughout the entire life stages, and gradually increased during 1-7 days, in a silkworm that was infected by N. bombycis, as determined by reverse-transcription PCR (RT-PCR). The
recombinant protein NbHSWP11 (rSWP11-HIS) was obtained and purified using gene cloning and prokaryotic expression. Western blotting analysis displayed NbHSWP11 expressed in the total mature spore
proteins and spore coat
proteins. Indirect immunofluorescence assay revealed NbHSWP11 located at the spore wall of mature spores and the spore coats. Furthermore, immune electron microscopy showed that NbHSWP11 localized in the cytoplasm of the sporont. Within the developmental process of N. bombycis, a portion of NbHSWP11 is targeted to the spore wall of sporoblasts and mature spores. However, most of NbHSWP11 distributes on the membraneous structures of the sporoblast and mature spore. In addition, using a host cell binding assay, native
protein NbHSWP11 in the supernatant of total soluble mature spore
proteins is shown to bind to the host cell BmE surface. Finally, an antibody blocking assay showed that purified rabbit antibody of NbHSWP11 inhibits spore adherence and decreases the adherence rate of spores by 20% compared to untreated spores. Collectively, the present results suggest that NbHSWP11 is involved in host cell adherence in vitro. Therefore NbHSWP11, which has a dnaJ domain, may modulate
protein assembly, disassembly, and translocation in N. bombycis.