Plasmodium sporozoites are extracellular forms introduced during mosquito bite that selectively invade mammalian hepatocytes. Sporozoites are delimited by a cell membrane that is linked to the underlying acto‐myosin molecular motor. While membrane proteins with roles in motility and invasion have been well studied, very little is known about proteins that maintain the sporozoite shape. We demonstrate that in Plasmodium berghei (Pb) a conserved hypothetical gene, PBANKA_1422900 specifies sporozoite structural integrity maintenance protein (SIMP) required for maintaining the sporozoite shape and motility. Sporozoites lacking SIMP exhibited loss of regular shape, extensive membrane blebbing at multiple foci, and membrane detachment. The mutant sporozoites failed to infect hepatocytes, though the altered shape did not affect the organization of cytoskeleton or inner membrane complex (IMC). Interestingly, the components of IMC failed to extend under the membrane blebs likely suggesting that SIMP may assist in anchoring the membrane to IMC. Endogenous C‐terminal HA tagging localized SIMP to membrane and revealed the C‐terminus of the protein to be extracellular. Since SIMP is highly conserved among Plasmodium species, these findings have important implications for utilizing it as a novel sporozoite‐specific vaccine candidate.

Tropical theileriosis is a lymphoproliferative disease caused by the intracellular schizonts of Theileria annulata, an apicomplexan parasite. It causes severe infection in cattle and the untreated cattle would possibly die within 3–4 weeks of infection. The chemotherapy for this disease is largely dependent on the use of hydroxynaphthoquinone, namely buparvaquone. There have been reports recently of the development of resistance against this drug in T. annulata . Hence, identification of new drug molecule(s) or repurposing of existing drug molecule(s) against T. annulata is quite important. Here, we present the screening of 400 compounds included in the open-access Pathogen box from Medicine for Malaria Venture (MMV) to discover the novel compounds with potential inhibitory activity against T. annulata infected bovine leucocytes. We identified two compounds, MMV000062 and MMV560185, with IC 50 values of 2.97 μM and 3.07 μM, respectively. MMV000062 and MMV560185 were found non-toxic to BoMac cells with CC 50 values 34 μM and > 100 μM, respectively. The therapeutic indices of these compounds, MMV000062 and MMV560185, were calculated as more than 33 and 11, respectively. Further, it was observed that the parasite-infected cells under long-term culture were unable to recover with these compounds. We further deciphered that MMV560185 kills the infected cell by activation of TNFR-1 mediated extrinsic pathway of the apoptosis. The phenotypic characteristics of apoptosis were confirmed by Transmission Electron Microscopy. Our results suggest that it may be possible to develop MMV560185 further for chemotherapeutics of tropical theilerosis.

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