Identification of a protein interacting with the spore wall protein SWP26 of Nosema bombycis in a cultured BmN cell line of silkworm.

Nosema bombycis is a silkworm parasite that causes severe economic damage to sericulture worldwide. It is the first microsporidia to be described in the literature, and to date, very little molecular information is available regarding microsporidian physiology and their relationships with their hosts. Therefore, the interaction between the microsporidia N. bombycis and its host silkworm, Bombyx mori, was analyzed in this study. The microsporidian spore wall proteins (SWPs) play a specific role in spore adherence to host cells and recognition by the host during invasion. In this study, SWP26 fused with enhanced green fluorescence protein (EGFP) was expressed in BmN cells by using a Bac-to-Bac expression system. Subsequently, the turtle-like protein of B. mori (BmTLP) was determined to interact with SWP26 via the use of anti-EGFP microbeads. This interaction was then confirmed by yeast two-hybrid analysis. The BmTLP cDNA encodes a polypeptide of 447 amino acids that includes a putative signal peptide of 27 amino acid residues. In addition, the BmTLP protein contains 2 immunoglobulin (IG) domains and 2 IGc2-type domains, which is the typical domain structure of IG proteins. The results of this study indicated that SWP26 interacts with the IG-like protein BmTLP, which contributes to the infectivity of N. bombycis to its host silkworm.