Characterization of a putative nuclear receptor from Onchocerca volvulus.

Steroids and retinoids are important regulators of development in invertebrates and vertebrates. The central mediators of action of these compounds are their cognate receptors, which together form a family of proteins known as the nuclear receptor family. Previous studies have demonstrated that the genome of Onchocerca volvulus encodes at least three members of the nuclear receptor family. Here, the characterization of one member of this family from O. volvulus, designated OvNR-2, is described. OvNR-2 was found to be most similar to a number of vertebrate retinoic acid receptors and to the Drosophila melanogaster EiP78c protein. Modeling studies suggest that OvNR-2 forms a boot shaped ligand-binding cavity of a shape and size that can bind steroids. Expression of the mRNA corresponding to OvNR-2 is tightly regulated in adult parasites, appearing only in the extended intrauterine microfilariae. The protein derived from expression of the OvNR-2 cDNA in a bacterial system is recognized by serum antibodies in a majority of individuals infected with O. volvulus.