Structure and Expression of an Adhesive Protein–like Molecule of Mosquito Invasive-stage Malarial Parasite

Invasion of the malarial parasite into a vector mosquito begins when the motile ookinete transverses the gut epithelium. Adhesive proteins that may mediate this invasive process have not been identified to date. We found that a molecule with an adhesive protein–like structure was expressed in the ookinete of Plasmodium berghei. This protein is structurally homologous to circumsporozoite protein and thrombospondin-related adhesive protein (TRAP)-related protein, CTRP, of Plasmodium falciparum. We named it P. berghei CTRP (PbCTRP) and report here its structure and manner of expression. PbCTRP has six integrin I region–like domains and seven thrombospondin-like domains in its putative extracellular region. This structure is similar to that of CTRP and TRAPs of malaria sporozoite. The putative transmembrane and cytoplasmic regions of PbCTRP, CTRP, and TRAP also have conserved amino acid sequences. PbCTRP is produced at least 10 h after fertilization when zygotes begin transformation to ookinetes. In the mature ookinete, PbCTRP is located mainly in the anterior cytoplasm. The staining pattern was also similar to TRAP in the sporozoite. We suggest that PbCTRP may play a role in ookinete invasive motility and belongs to a protein family together with TRAP and other structurally related proteins of apicomplexan parasites.