Identification and molecular characterization of a novel stage-specific surface protein of Trypanosoma congolense epimastigotes

The cattle pathogen Trypanosoma congolense expresses life cycle stage-specific surface molecules involved in adaptation to different host and vector environments. Here we report the discovery and molecular characterization of a novel stage-specific GPI-anchored surface glycoprotein that is selectively expressed in the epimastigote (EMF) life cycle stage of T. congolense. Culture supernatants of EMF but not of procyclic culture forms (PCFs) promoted adhesion of PCF parasites in an in vitro assay. Biosynthetic labeling experiments showed that these EMF culture supernatants contained a 100 kDa trypanosome-derived protein that was not present in supernatants from PCF. We named this molecule “congolense epimastigote-specific protein” (CESP). The gene encoding CESP was isolated from an EMF cDNA library after immunoscreening. The multicopy gene had a 2070-bp open reading frame that encodes a polypeptide of 689 amino acids with a predicted mass of 72.9 kDa. The discrepancy between the predicted (72.9 kDa) and observed (100 kDa) masses may be explained partially by glycosylation of the molecule which has six potential N-glycosylation sites and a predicted GPI anchor. Indeed, metabolic labeling of CESP with [3H] ethanolamine revealed that CESP was a GPI-anchored protein. Confocal laser scanning microscopy showed that CESP was expressed only on the surface of the EMF stage of the parasite. The identification of CESP as a unique component of culture supernatants from EMF and that such supernatants can confer plastic-adhesive ability on PCF suggest that CESP is worth further investigation as an adhesion molecule that perhaps allows T. congolense EMF to adhere to the tsetse proboscis.