C-Mannosyltransferase Is Essential for Malaria Transmission in Plasmodium berghei.

C-Mannosylation of the thrombospondin type I repeat (TSR) domains is one of the most important factors involved in their function. It occurs on the first tryptophan of the WXXWXXC conserved motif where the tryptophan is usually surrounded by arginine or lysine forming the ligand-binding stretch of this sticky domain. It is found in its canonical or modified forms in many Plasmodium proteins. TSR containing proteins such as thrombospondin-like anonymous protein (TRAP), circumsporozoite protein (CSP), CSP and TRAP related protein (CTRP), and secreted protein with altered thrombospondin repeat (SPATR) have all been shown to be important for various parasite processes and life cycle stages. Here, we show that C-mannosylation catalyzing enzyme C-mannosyltransferase (CmanT) plays an essential role in malaria transmission in Plasmodium berghei. Disruption of the CmanT does not affect asexual blood stage propagation or gametocyte development but abolishes the formation of oocysts in mosquitoes. CmanT knockout (CmanT-) parasites showed normal ookinete formation; however, these ookinetes failed in their ability to glide. CmanT- was complemented by reintroducing the gene, restoring mosquito transmission to wild-type level. We also investigated the effect of C-mannosylation on the folding and heparin-binding capacity of the Plasmodium falciparum TRAP TSR domain in silico, which suggested that this phenotype should be due to its involvement in the global stabilization of TSR residue side chain interactions.