A Conserved Plasmodium Structural Integrity Maintenance Protein (SIMP) is associated with sporozoite membrane and is essential for maintaining shape and infectivity

The novel Plasmodium berghei protein S14 is essential for sporozoite gliding motility and infectivity

Plasmodium sporozoites are the infective forms of the malaria parasite in the mosquito and vertebrate host. Gliding motility allows sporozoites to migrate and invade mosquito salivary glands and mammalian hosts. Motility and invasion are powered by an actin-myosin motor complex linked to the glideosome, which contains glideosome-associated proteins (GAPs), MyoA and the myosin A tail-interacting protein (MTIP). However, the role of several proteins involved in gliding motility remains unknown. We identified that the S14 gene is upregulated in sporozoite from transcriptome data of Plasmodium yoelii and further confirmed its transcription in P. berghei sporozoites using real-time PCR. C-terminal 3×HA-mCherry tagging revealed that S14 is expressed and localized on the inner membrane complex of the sporozoites. We disrupted S14 in P. berghei and demonstrated that it is essential for sporozoite gliding motility, and salivary gland and hepatocyte invasion. The gliding and invasion-deficient S14 knockout sporozoites showed normal expression and organization of inner membrane complex and surface proteins. Taken together, our data show that S14 plays a role in the function of the glideosome and is essential for malaria transmission.

A conserved malaria parasite protein required for maintenance of sporozoite cell shape and transmission

Malaria parasites are transmitted by mosquitoes and a substantial part of the parasite's complex life cycle takes place inside the insect. Parasite transmission starts with the uptake of parasite stages called gametocytes from the vertebrate host with the blood meal of a female vector mosquito, completing several weeks later with the injection of parasite stages called sporozoites into the vertebrate host by mosquito bite. The sporozoites form in their thousands inside ookinete-derived oocysts situated on the abluminal side of the mosquito midgut epithelium by a process of cell division known as sporogony. After their formation, sporozoites egress from the oocyst into the haemolymph, invade the salivary glands and mature to become infective to the vertebrate. This MicroCommentary reviews recent reports describing a conserved plasma membrane-associated protein of Plasmodium berghei, PBANKA_1422900, and its role in maintaining the shape and structural integrity of sporozoites in salivary glands and during inoculation into the vertebrate host. Combined results from three separate studies provide mechanistic insights into how this protein achieves structural maintenance of the sporozoite, and how in turn this promotes the sporozoite's ability to overcome several physical obstacles and allow it to establish infection in the vertebrate.