Development of an approach to analyze the interaction between Nosema bombycis (microsporidia) deproteinated chitin spore coats and spore wall proteins.

Nosema bombycis is an obligate intracellular parasite of the Bombyx mori insect. The spore wall of N. bombycis is composed of an electron-dense proteinaceous outer layer and an electron-transparent chitinous inner layer, and the spore wall is connected to the plasma membrane. In this study, the deproteinated chitin spore coats (DCSCs) were acquired by boiling N. bombycis in 1M NaOH. Under a transmission electron microscope, the chitin spore coat resembles a loosely curled ring with strong refractivity; organelles and nuclei were not observed inside the spore. The anti-SWP25, 26, 30 and 32 antibodies were used to detect whether spore wall proteins within the total soluble and mature spore proteins could bind to the DCSCs. Furthermore, a chitin binding assay showed that within the total soluble and mature spore proteins, the SWP26, SWP30 and SWP32 spore wall proteins, bound to the deproteinated chitin spore coats, although SWP25 was incapable of this interaction. Moreover, after the DCSCs were incubated with the alkali-soluble proteins, the latter were obtained by treating N. bombycis with 0.1M NaOH. Following this treatment, SWP32 was still capable of binding the DCSCs, while SWP26 and SWP30 were unable to bind. Collectively, the DCSCs are useful for investigating the arrangement of spore wall proteins, and they shed light on how the microsporidia spore wall is self-assembled.