Fig. 10.

A working model for the biological process of GP900 in sporozoites. GP900 protein (a) is stored in the secretory organelle micronemes in sporozoites in oocysts before excystation (b). After excystation and during invasion, GP900 in the microneme vesicles enters the secretory pathway (c, step 1). Before the secretory vesicles reach to the plasma membrane, the short C-terminal cytoplasmic domain of GP900 is cleaved (step 2). The vesicles reach and fused with the plasma membrane (step 3), and cleaved GP900 molecules are discharged to the extracellular space (step 4). Some secreted GP900 molecules adhere to the surface of the plasma membrane due to the general adhesive property of the glycoprotein, while other molecules are shed into the surrounding microenvironment. The transmembrane domain of GP900 contains conserved amino acids (purple) near the non-cytoplasmic side for intramembrane cleavage by rhomboid peptidases (d). Abbreviations: DG, Dense granules; IMC, inner membrane complex; MN, microneme; Nuc, nucleus; PM, plasma membrane