The guanine protein coupled receptor rhodopsin is developmentally regulated in the free-living stages of Schistosoma mansoni

Schistosoma mansoni parasites inhabit three distinct environments including water, intermediate molluscan hosts, and definitive vertebrate hosts. Dete rmining how schistosomes interact with these environments may be one mechan ism by which suitable vaccines or novel chemotherapeutic targets will be id entified. Towards this end, we describe the identification of a 36-kDa S. m ansoni protein that shares extensive sequence similarity to light absorbing rhodopsin guanine protein coupled receptors (GPCRs). This protein, S. mans oni rhodopsin (SmRHO), is the first molecularly characterized GPCR describe d in schistosomes. Sequence analysis reveals that SmRHO shares extensive ph ylogenetic conservation among rhodopsins/opsins expressed in water-dwelling invertebrates, possibly indicative of orthology. We demonstrate here that SmRHO is expressed in the free-living light responsive miracidia and cercar ia stages and is down-regulated in the adult, vertebrate residing forms. Mo reover, we show that SmRHO is localized to sub-tegumental structures found towards the anterior end of cercariae. As SmRHO may be implicated in schist osome photoreception processes, we have begun a search for additional paras ite encoded GPCR super-family members, which may be associated with chemore ception, chemotaxis, and olfaction. Identifying and characterizing new GPCR s may uncover hidden aspects of parasite biology useful towards the develop ment of novel intervention strategies. (C) 2001 Elsevier Science B.V. All r ights reserved.