Secreted protein with altered thrombospondin repeat (SPATR) is essential for asexual blood stages but not required for hepatocyte invasion by the malaria parasite Plasmodium berghei

Abstract

Upon entering its mammalian host, the malaria parasite productively invades two distinct cell types, that is, hepatocytes and erythrocytes during which several adhesins/invasins are thought to be involved. Many surface‐located proteins containing thrombospondin Type I repeat (TSR) which help establish host–parasite molecular crosstalk have been shown to be essential for mammalian infection. Previous reports indicated that antibodies produced against Plasmodium falciparum secreted protein with altered thrombospondin repeat (SPATR) block hepatocyte invasion by sporozoites but no genetic evidence of its contribution to invasion has been reported. After failing to generate Spatr knockout in Plasmodium berghei blood stages, a conditional mutagenesis system was employed. Here, we show that SPATR plays an essential role during parasite's blood stages. Mutant salivary gland sporozoites exhibit normal motility, hepatocyte invasion, liver stage development and rupture of the parasitophorous vacuole membrane resulting in merosome formation. But these mutant hepatic merozoites failed to establish a blood stage infection in vivo. We provide direct evidence that SPATR is not required for hepatocyte invasion but plays an essential role during the blood stages of P. berghei.

Downregulation of the secreted protein with an altered thrombospondin repeat (SPATR) impacts the infectivity of malaria sporozoites

“…Thus, it is plausible that there is a density threshold within the salivary glands required for the maximization of sporozoite fitness and infectivity. Indeed, SPATR conditional knockout sporozoites generated using the Flp-FRT system were capable of invading the salivary glands and showed no liver stage defects (19). Nevertheless, it is important to note that these recombinase-based systems often fail to achieve full deletion of the target sequence within a population (63,64), which could be of particular significance in the context of secreted proteins.…”

“…However, no defects in sporozoite infectivity to the mosquito or hepatocytes were detected using this conditional KO line (19). In fact, upon hepatocyte infection with sporozoites, merozoites were formed but failed to infect red blood cells (19).…”

“…The secreted protein with an altered thrombospondin repeat (SPATR) contains two adhesive domains: an atypical thrombospondin type-1 repeat (TSR) and a Type II epidermal growth factor (EGF)-like domain (16)(17)(18). It is conserved across Plasmodium species and has several orthologues among the Apicomplexa phylum (19). Although its gene is transcribed in all invasive stages (sporozoites, merozoites and ookinetes) (20,21), SPATR levels are upregulated in mature sporozoites of both human and rodent infecting Plasmodium species (12,15).…”

“…(19,22). The stage-specific conditional KO of spatr using a flippase-flippase recombination target (Flp-FRT) system (23), which has been used to study gene function in sporozoites (24), consolidated the indispensability of SPATR for the P. berghei blood stage (19).…”

Tryptophan C-mannosylation is critical for Plasmodium falciparum transmission

“…The ten Plasmodium proteins of the TRAP adhesin family possess TSR domains and play essential roles in host cell infection during asexual 17 , sexual 18,19 , ookinete [20][21][22] and sporozoite [23][24][25][26][27][28][29] stages of the lifecycle. These proteins are expressed on the cell surface and, with the exception of 'circumsporozoite protein' (CSP), are believed to provide a proteinaceous connection between the intracellular actomyosin motor and the extracellular environment to generate forces for parasite gliding motility, invasion and egress from host cells.…”