Macrophage-expressed gene 1 MPEG1/Perforin-2 (PRF2) is an ancient metazoan protein belonging to the Membrane Attack Complex/Perforin (MACPF) branch of the MACPF/Cholesterol Dependent Cytolysin (CDC) ...superfamily of pore-forming proteins (PFPs). MACPF/CDC proteins are a large and extremely diverse superfamily that forms large transmembrane aqueous channels in target membranes. In humans, MACPFs have known roles in immunity and development. Like perforin (PRF) and the membrane attack complex (MAC), MPEG1 is also postulated to perform a role in immunity. Indeed, bioinformatic studies suggest that gene duplications of MPEG1 likely gave rise to PRF and MAC components. Studies reveal partial or complete loss of MPEG1 causes an increased susceptibility to microbial infection in both cells and animals. To this end, MPEG1 expression is upregulated in response to proinflammatory signals such as tumor necrosis factor α (TNFα) and lipopolysaccharides (LPS). Furthermore, germline mutations in MPEG1 have been identified in connection with recurrent pulmonary mycobacterial infections in humans. Structural studies on MPEG1 revealed that it can form oligomeric pre-pores and pores. Strikingly, the unusual domain arrangement within the MPEG1 architecture suggests a novel mechanism of pore formation that may have evolved to guard against unwanted lysis of the host cell. Collectively, the available data suggest that MPEG1 likely functions as an intracellular pore-forming immune effector. Herein, we review the current understanding of MPEG1 evolution, regulation, and function. Furthermore, recent structural studies of MPEG1 are discussed, including the proposed mechanisms of action for MPEG1 bactericidal activity. Lastly limitations, outstanding questions, and implications of MPEG1 models are explored in the context of the broader literature and in light of newly available structural data.
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•All Babesia perforin-like proteins have the critical domains necessary for pore formation.•Babesia bovis PLP1 is expressed and exposed to the bovine immune system.•Babesia bovis PLP1 ...has high hemolytic capacity under a wide range of conditions.•A B. bovis Δplp1 line shows a slower growth rate in in vitro cultures.•Some Δplp1 parasites accumulate in erythrocytes, implying a role for PLP1 in egress.
Bovine babesiosis is a tick-borne disease caused by apicomplexan parasites of the Babesia genus that represents a major constraint to livestock production worldwide. Currently available vaccines are based on live parasites which have archetypal limitations. Our goal is to identify candidate antigens so that new and effective vaccines against Babesia may be developed. The perforin-like protein (PLP) family has been identified as a key player in cell traversal and egress in related apicomplexans and it was also identified in Babesia, but its function in this parasite remains unknown. The aim of this work was to define the PLP family in Babesia and functionally characterize PLP1, a representative member of the family in Babesia bovis. Bioinformatic analyses demonstrate a variable number of plp genes (four to eight) in the genomes of six different Babesia spp. and conservation of the family members at the secondary and tertiary structure levels. We demonstrate here that Babesia PLPs contain the critical domains present in other apicomplexan PLPs to display the lytic capacity. We then focused on the functional characterization of PLP1 of B. bovis, both in vitro and in vivo. PLP1 is expressed and exposed to the host immune system during infection and has high hemolytic capacity under a wide range of conditions in vitro. A B. bovis plp1 knockout line displayed a decreased growth rate in vitro compared with the wild type strain and a peculiar phenotype consisting of multiple parasites within a single red blood cell, although at low frequency. This phenotype suggests that the lack of PLP1 has a negative impact on the mechanism of egression of the parasite and, therefore, on its capacity to proliferate. It is possible that PLP1 is associated with other proteins in the processes of invasion and egress, which were found to have redundant mechanisms in related apicomplexans. Future work will be focused on unravelling the network of proteins involved in these essential parasite functions.
Effects of MACPF/CDC proteins on lipid membranes Gilbert, Robert J. C.; Mikelj, Miha; Dalla Serra, Mauro ...
Cellular and molecular life sciences : CMLS,
06/2013, Volume:
70, Issue:
12
Journal Article
Peer reviewed
Recent work on the MACPF/CDC superfamily of pore-forming proteins has focused on the structural analysis of monomers and pore-forming oligomeric complexes. We set the family of proteins in context ...and highlight aspects of their function which the direct and exclusive equation of oligomers with pores fails to explain. Starting with a description of the distribution of MACPF/CDC proteins across the domains of life, we proceed to show how their evolutionary relationships can be understood on the basis of their structural homology and re-evaluate models for pore formation by perforin, in particular. We furthermore highlight data showing the role of incomplete oligomeric rings (arcs) in pore formation and how this can explain small pores generated by oligomers of proteins belonging to the family. We set this in the context of cell biological and biophysical data on the proteins’ function and discuss how this helps in the development of an understanding of how they act in processes such as apicomplexan parasites gliding through cells and exiting from cells.
Perforin-Like Proteins of Apicomplexan Parasites Sassmannshausen, Juliane; Pradel, Gabriele; Bennink, Sandra
Frontiers in cellular and infection microbiology,
09/2020, Volume:
10
Journal Article
Peer reviewed
Open access
Perforins are secreted proteins of eukaryotes, which possess a membrane attack complex/perforin (MACPF) domain enabling them to form pores in the membranes of target cells. In higher eukaryotes, they ...are assigned to immune defense mechanisms required to kill invading microbes or infected cells. Perforin-like proteins (PLPs) are also found in apicomplexan parasites. Here they play diverse roles during lifecycle progression of the intracellularly replicating protozoans. The apicomplexan PLPs are best studied in
and
, the causative agents of malaria and toxoplasmosis, respectively. The PLPs are expressed in the different lifecycle stages of the pathogens and can target and lyse a variety of cell membranes of the invertebrate and mammalian hosts. The PLPs thereby either function in host cell destruction during exit or in overcoming epithelial barriers during tissue passage. In this review, we summarize the various PLPs known for apicomplexan parasites and highlight their roles in
and
lifecycle progression.
Astrotactins (ASTNs) and Bone morphogenetic protein/retinoic acid inducible neural-specific proteins (BRINPs) are two groups of Membrane Attack Complex/Perforin (MACPF) superfamily proteins that show ...overlapping expression in the developing and mature vertebrate nervous system. ASTN(1–2) and BRINP(1–3) genes are found at conserved loci in humans that have been implicated in neurodevelopmental disorders (NDDs).
Here we review the tissue distribution and cellular localization of these proteins, and discuss recent studies that provide insight into their structure and interactions. We highlight the genetic relationships and co-expression of Brinps and Astns; and review recent knock-out mouse phenotypes that indicate a possible overlap in protein function between ASTNs and BRINPs.
Summary
Plant immune responses triggered upon recognition of microbe‐associated molecular patterns (MAMPs) typically restrict pathogen growth without a host cell death response. We isolated two ...Arabidopsis mutants, derived from accession Col‐0, that activated cell death upon inoculation with nonadapted fungal pathogens. Notably, the mutants triggered cell death also when treated with bacterial MAMPs such as flg22. Positional cloning identified NSL1 (Necrotic Spotted Lesion 1) as a responsible gene for the phenotype of the two mutants, whereas nsl1 mutations of the accession No‐0 resulted in necrotic lesion formation without pathogen inoculation. NSL1 encodes a protein of unknown function containing a putative membrane‐attack complex/perforin (MACPF) domain. The application of flg22 increased salicylic acid (SA) accumulation in the nsl1 plants derived from Col‐0, while depletion of isochorismate synthase 1 repressed flg22‐inducible lesion formation, indicating that elevated SA is needed for the cell death response. nsl1 plants of Col‐0 responded to flg22 treatment with an RBOHD‐dependent oxidative burst, but this response was dispensable for the nsl1‐dependent cell death. Surprisingly, loss‐of‐function mutations in PEN2, involved in the metabolism of tryptophan (Trp)‐derived indole glucosinolates, suppressed the flg22‐induced and nsl1‐dependent cell death. Moreover, the increased accumulation of SA in the nsl1 plants was abrogated by blocking Trp‐derived secondary metabolite biosynthesis, whereas the nsl1‐dependent hyperaccumulation of PEN2‐dependent compounds was unaffected when the SA biosynthesis pathway was blocked. Collectively, these findings suggest that MAMP‐triggered immunity activates a genetically programmed cell death in the absence of the functional MACPF domain protein NSL1 via Trp‐derived secondary metabolite‐mediated activation of the SA pathway.
Significance Statement
Plant immune responses triggered by recognition of microbe‐associated molecular patterns (MAMPs) typically restrict pathogen growth without host cell death. Here, by characterizing Arabidopsis mutants that do activate cell death upon MAMP recognition, we show that a membrane‐attack complex/perforin (MACPF) domain protein is required to suppress MAMP‐triggered antimicrobial metabolism that activates the salicylic acid signaling leading to a cell death response.
The eggshell serves as a depository for proteins that play an important role in early embryonic development. In particular, the Drosophila eggshell is responsible for transferring asymmetries from ...the egg chamber to specify the regions at both ends of the embryo through the uneven activation of the Torso (Tor) receptor in its membrane. This process relies on the restricted expression of the gene torso-like (tsl) in subpopulations of follicle cells during oogenesis and its protein accumulation at both poles of the eggshell, but it is not known how this signal is transmitted to the embryo. Here, we show that Tsl accumulates at the embryonic plasma membrane, even in the absence of the Tor receptor. However, during oogenesis, we detected Tsl accumulation only at the eggshell. These results suggest that there is a two-step mechanism to transfer the asymmetric positional cues from the egg chamber into the early embryo: initial anchoring of Tsl at the eggshell as it is secreted, followed by its later translocation to the egg plasma membrane, where it enables Tor receptor activation. Translocation of anchored determinants from the eggshell might then regulate the spatial and temporal control of early embryonic developmental processes.
•Perforin-2 is expressed in human macrophages with two isoforms.•Perforin-2a is localized on endosome-like vesicles and triggered to fuse with lysosomes by pro-inflammatory stimuli.•Perforin-2b is ...triggered for high expression and secretion by LPS stimulation.
Perforin-2 is constitutively expressed in macrophages that are required for bacterial control. In this study, we found that perforin-2 is expressed in human macrophages with two isoforms: full-length perforin-2a and a splice variant, perforin-2b. Two isoforms show different subcellular distributions. Perforin-2a was predominantly localized to the membrane of endosome-like vesicles by a C-terminal transmembrane domain. In contrast, the short isoform perforin-2b lacking the transmembrane domain failed to localize to the membrane of vesicles. Furthermore, we determined that the pro-inflammatory stimuli LPS and TNF-α induced perforin-2a expression via the NF-κB pathway and triggered perforin-2a vesicles fusion with lysosomes. On the other hand, we detected the secretion of perforin-2b in response to LPS stimulation. Taken together, our data provide the evidence that membrane-bound and secretory isoforms of perforin-2 are present in human macrophages and may play important roles in immune defense.
The evolution of early multicellular eukaryotes 400–500 million years ago required a defensive strategy against microbial invasion. Pore-forming proteins containing the ...membrane-attack-complex-perforin (MACPF) domain were selected as the most efficient means to destroy bacteria or virally infected cells. The mechanism of pore formation by the MACPF domain is distinctive in that pore formation is purely physical and unspecific. The MACPF domain polymerizes, refolds, and inserts itself into bilayer membranes or bacterial outer cell walls. The displacement of surface lipid/carbohydrate molecules by the polymerizing MACPF domain creates clusters of large, water-filled holes that destabilize the barrier function and provide access for additional anti-bacterial or anti-viral effectors to sensitive sites that complete the destruction of the invader via enzymatic or chemical attack. The highly efficient mechanism of anti-microbial defense by a combined physical and chemical strategy using pore-forming MACPF-proteins has been retargeted during evolution of vertebrates and mammals for three purposes: (1) to kill extracellular bacteria C9/polyC9 evolved in conjunction with complement, (2) to kill virus infected and cancer cells perforin-1/polyperforin-1 CTL evolved targeted by NK and CTL, and (3) to kill intracellular bacteria transmembrane perforin-2/putative polyperforin-2 evolved targeted by phagocytic and nonphagocytic cells. Our laboratory has been involved in the discovery and description of each of the three pore-formers that will be reviewed here.
•Ostreolysin A/pleurotolysin B mixture forms ion-conducting pores in cell membranes.•Single-pore conductance was 600pS in N18 cells, and 485pS in CHO cells.•The proteins induce colloid-osmotic ...hemolysis, inhibited by PEGs >2000.
Proteins from the oyster mushroom, 15kDa ostreolysin A (OlyA), and 59kDa pleurotolysin B (PlyB) with a membrane attack complex/perforin (MACPF) domain, damage cell membranes as a binary cytolytic pore-forming complex. Measurements of single-channel conductance and transmembrane macroscopic current reveal that OlyA/PlyB form non-selective ion-conducting pores with broad, skewed conductance distributions in N18 neuroblastoma and CHO-K1 cell membranes. Polyethylene-glycol 8000 (hydrodynamic radius of 3.78nm) provides almost complete osmotic protection against haemolysis, which strongly suggests a colloid-osmotic type of erythrocyte lysis. Our data indicate that OlyA/PlyB form transmembrane pores of varied sizes, as other pore-forming proteins with a MACPF domain.
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