Plasmodium berghei: Plasmodium perforin-like protein 5 is required for mosquito midgut invasion in Anopheles stephensi

Abstract

During its life cycle the malarial parasite Plasmodium forms three invasive stages which have to invade different and specific cells for replication to ensue. Invasion is vital to parasite survival and consequently proteins responsible for invasion are considered to be candidate vaccine/drug targets. Plasmodium perforin-like proteins (PPLPs) have been implicated in invasion because they contain a predicted pore-forming domain. Ookinetes express three PPLPs, and one of them (PPLP3) has previously been shown to be essential for mosquito midgut invasion. In this study we show through phenotypic analysis of loss-of-function mutants that PPLP5 is equally essential for mosquito infection. Δpplp5 ookinetes cannot invade midgut epithelial cells, but subsequent parasite development is rescued if the midgut is bypassed by injection of ookinetes into the hemocoel. The indistinguishable phenotypes of Δpplp5 and Δpplp3 ookinetes strongly suggest that these two proteins contribute to a common process.

The development of malaria parasites in the mosquito midgut

“…Other microneme proteins assigned to midgut traversal of P . berghei ookinetes include SOAP, WARP and CelTOS (cell‐traversal protein for ookinetes and sporozoites) (Yuda et al ., 2001; Dessens et al ., 2003; Kadota et al ., 2004; Li et al ., 2004; Kariu et al ., 2006; Ecker et al ., 2007, 2008; Kaneko et al ., 2015; Wirth et al ., 2015) (Table 1). …”

Apicomplexan perforin-like proteins

“…Here we present an overview of this important protein family from a structural, functional and phylogenetic perspective across the Apicomplexa. 15 ) all share similar domain architectures with a N-terminal region of variable length followed by a centrally located MACPF domain and ending in a β-pleated sheet-rich domain unique to the apicomplexa (Fig. 1).…”

“…Disruption of PPLP5, a second MACPF protein expressed in ookinetes, yielded an identical phenotype of ookinetes unable to invade or traverse the midgut epithelium. 15 The mirrored phenotype of PPLP3 and PPLP5 knockout strains suggests that these two PPLPs may interact to accomplish midgut traversal, analogous to the interaction of multiple MACPF-domain proteins (C6-C9) to form the membrane attack complex. Proteomic evidence suggests the expression of a third MACPF-domain protein (PPLP4) in ookinetes but it has not been functionally characterized to date.…”

Cellular and molecular interactions between the apicomplexan parasitesPlasmodiumandTheileriaand their host cells

“…In exiting the midgut, the ookinete traverses a number of midgut epithelial cells before reaching the basal lamina and rounding up to become an oocyst (Zieler & Dvorak, 2000). The process of cell transmigration is similar to that displayed by sporozoites in traversing hepatocytes, again requiring the action of perforin-like proteins (Ecker et al, 2007;Ishino et al, 2005;Kadota et al, 2004). In both processes, a prerequisite of parasite transmigration is secretion of the parasite protein CelTOS into the cytoplasm of the traversed cell (Kariu et al, 2006).…”