Advances in understanding red blood cell modifications by Babesia
Fig 5
Schematic of the protein export pathway in Babesia iRBC.
The appointed soluble proteins for the export are being recruited into ER, cleaved by signal peptidase, and likely followed by cleavage of PLM. Transmembrane-containing proteins such as VESA1 or mtm are inserted into the ER membrane. These proteins are loaded into secretory vesicles of the ER-Golgi pathway, which are being transferred to spherical bodies (in the case of spherical body proteins: SBP1, SBP2, SBP3, SBP4, VEAP, and mtm) or directly to parasite plasma membrane (in the case of VESA1). Soluble proteins are released to RBC cytoplasm, while integral protein needs to be extracted from PPM, which may involve protein translocation. Soluble protein could reach the target by diffusion, while membrane proteins are carried out to the target destination through vesicles or in complex with chaperones. It is noted that this scheme is speculative. ER, endoplasmic reticulum; iRBC, infected RBC; PLM, PEXEL-like motif; PPM, parasite plasma membrane; RBC, red blood cell; RPM, RBC plasma membrane; VESA1, variant erythrocyte surface antigen 1.
