Characterization of proteins localized to a subcellular compartment associated with an alternate secretory pathway of the malaria parasite.

Monoclonal antibodies recognizing proteins localized to a unique subcellular compartment within the malaria parasite are described in this report. These monoclonal antibodies recognize Plasmodium falciparum proteins of 68, 45 and 22 kDa proteins which are also conserved in rodent Plasmodium species. Co-localization studies indicate that these proteins are located in a brefeldin A-induced compartment which was previously proposed to be an early step in the export of proteins from the parasite into the infected erythrocyte. COPII coat proteins, Sar1p and Sec31p, and the endoplasmic reticulum-associated chaperone, BiP, all partially co-localize with the 68 and 22 kDa proteins, thus suggesting that this subcellular compartment has some similarities to the endoplasmic reticulum or that this compartment represents a domain of the endoplasmic reticulum. The 68 and 22 kDa proteins are highly soluble in non-ionic detergent and are likely to be located within the lumen of a membrane-bound compartment. These proteins found within this subcellular compartment are present throughout the blood stage from very early rings to segmenters. The results of this study further substantiate the existence of an alternate secretory pathway in the malaria parasite which plays a role in the export of proteins into the host erythrocyte.