Construction and heterologous overexpression of two chimeric proteins carrying outer hydrophilic loops of Vairimorpha ceranae and Nosema bombycis ATP/ADP carriers

Abstract

Microsporidia Nosema bombycis and Vairimorpha ceranae cause destructive epizootics of honey bees and silkworms. Insufficient efficiency of the antibiotic fumagillin against V. ceranae, its toxicity and the absence of effective methods of N. bombycis treatment demand the discovery of novel strategies to suppress infections of domesticated insects. RNA interference is one such novel treatment strategy. Another one implies that the intracellular development of microsporidia may be suppressed by single-chain antibodies (scFv fragments) against functionally important parasite proteins. Important components of microsporidian metabolism are non-mitochondrial, plastidic-bacterial ATP/ADP carriers. These membrane transporters import host-derived ATP and provide the capacity to pathogens for energy parasitism. Here, we analyzed membrane topology of four V. ceranae and three N. bombycis ATP/ADP transporters to construct two fusion proteins carrying their outer hydrophilic loops contacting with infected host cell cytoplasm. Interestingly, full-size genes of N. bombycis transporters may be derived from the Asian swallowtail Papilio xuthus genome sequencing project. Synthesis of the artificial genes was followed by overexpression of recombinant proteins in E. coli as insoluble inclusion bodies. The gene fragments encoding the loops of individual transporters were also effectively expressed in bacteria. The chimeric antigens may be used to construct immune libraries or select microsporidia-suppressing scFv fragments from synthetic, semisynthetic, naïve and immune antibody libraries. A further expression of such antibodies in insect cells may increase their resistance to microsporidial infections.