A DOC2 Protein Identified by Mutational Profiling Is Essential for Apicomplexan Parasite Exocytosis

Marc-Jan Gubbels et al. Science. (2012). 335(6065):218-21.

Speaker: Mei-Ling Lai (賴玫伶)                                   Time: 15:10~16:00, May 30, 2011

Commentator: Dr. Chih-Li Hsu (胥直利博士)             Place: Room 601

Abstract

        Exocytosis is essential to the lytic cycle of apicomplexan parasites and required for the pathology of apicomplexan diseases such as malaria caused by Plasmodium spp. Tandem C2 domain proteins responded to Ca²⁺-mediated exocytosis¹. Previous study shown the phenotype of aToxoplasma gondii temperature-sensitive mutant (F-P2) displayed inability to egress. However, the mechanism is still unclear. In this study, authors found that F-P2 impaired in host cell invasion was pinpointed to a defect in microneme secretion. In order to identify the sole gene responsible for the microneme secretion defect. Using of whole-genome sequencing, the authors identified gene TGGT1_049850, which contains Ca²⁺-dependent membrane-binding C2 domains. And then they found the orthologous function of TGGT1_049850 in microneme secretion and named TgDOC2.1.Structural prediction suggests that TgDOC2.1 can bind Ca²⁺ ions through conserved Asp residues in the C2 domains². They constructed a and engineered into Plasmodium falciparum, via genetic fusion of a destabilizing domain (DD) to conditional allele of the orthologous gene C terminus. The DD fusion protein is stabilized by the synthetic ligand Shld1 and targeted for degradation in absence of Shld1. To evaluate the contribution of PfDOC2.1 to parasite invasion, parasite invasion to red blood cells was decreased as compared with parasites rescued by the addition of Shld1. In addention, in the absence of Shld1, release of microneme protein was decreased. In brief, The C2 domains in cytosolic DOC2 proteins triggering microneme secretion is essential for Apicomplexan parasite exocytosis.

Reference

1.         Friedrich, R., Yeheskel, A. & Ashery, U. DOC2B, C2 domains, and calcium: A tale of intricate interactions. Molecular neurobiology 41, 42-51 (2010).

2.         Martens, S. & McMahon, H.T. Mechanisms of membrane fusion: disparate players and common principles. Nature reviews. Molecular cell biology 9, 543-556 (2008).