An ER CREC family protein regulates the egress proteolytic cascade in malaria parasites

Abstract

The endoplasmic reticulum (ER) is thought to play an essential role during egress of malaria parasites because the ER is assumed to be the calcium (Ca2+) signaling hub and required for biogenesis of egress-related organelles. However, no proteins localized to the parasite ER have been shown to play a role in egress of malaria parasites. In this study, we generated conditional mutants of the Plasmodium falciparumEndoplasmic Reticulum-resident Calcium-binding protein (PfERC), a member of the CREC family. Knockdown of PfERC shows that this gene is essential for asexual growth of P. falciparum. Analysis of the intraerythrocytic lifecycle revealed that PfERC is essential for parasite egress but not required for protein trafficking or Ca2+ storage. We found that PfERC knockdown prevents the rupture of the parasitophorous vacuole membrane. This is because PfERC knockdown inhibited the proteolytic maturation of the subtilisin-like serine protease, SUB1. Using double mutant parasites, we show that PfERC is required for the proteolytic maturation of the essential aspartic protease, Plasmepsin X, which cleaves SUB1. Further, we show that processing of substrates downstream of the proteolytic cascade is inhibited by PfERC knockdown. Thus, these data establish the ER-resident CREC family protein, PfERC, as a key early regulator of the egress proteolytic cascade of malaria parasites.

A potential third‐order role of the host endoplasmic reticulum as a contact site in interkingdom microbial endosymbiosis and viral infection

“…A feature of the ER-mitochondria MCSs (second-order) is the mitochondria-directed Ca 2+ hotspots released from the ER (reviewed in Almeida and Amaral, 2020); the mitochondria then sense the released Ca 2+ as a signal to regulate essential functions, such as metabolism, energy production and apoptosis (reviewed in Marchi et al, 2018). Interestingly, ER calcium (Ca 2+ )-mediated signalling pathways have been suggested to be involved in 'third-order' ER interactions, for example in specific life cycle stages of parasitic apicomplexans, such as T. cruzi (described in section Metazoan host ER interface with parasitic protist apicomplexans), T. gondii and P. falciparum (Nagamune et al, 2007;Moreno et al, 2011;Lourido and Moreno, 2015;Fierro et al, 2018). Disruption of calcium homeostasis by bacterial pathogens, such as Shigella invasion and Chlamydia extrusions, is also known (Tran Van Nhieu et al, 2018).…”

Knock-sideways by inducible ER retrieval enables a novel approach for studyingPlasmodiumsecreted proteins

“…Similar to other eukaryotes, ER retention of secreted reporters or chimeric proteins can be achieved in Plasmodium spp. by a C-terminal KDEL or functional variants (17)(18)(19)(20)(21)(22).…”