Cryo-EM structures of perforin-2 in isolation and assembled on a membrane suggest a mechanism for pore formation.

Perforin-2 (PFN2, MPEG1) is a key pore-forming protein in mammalian innate immunity restricting intracellular bacteria proliferation. It forms a membrane-bound pre-pore complex that converts to a pore-forming structure upon acidification; but its mechanism of conformational transition has been debated. Here we used cryo-electron microscopy, tomography and subtomogram averaging to determine structures of PFN2 in pre-pore and pore conformations in isolation and bound to liposomes. In isolation and upon acidification, the pre-assembled complete pre-pore rings convert to pores in both flat ring and twisted conformations. On membranes, in situ assembled PFN2 pre-pores display various degrees of completeness; whereas PFN2 pores are mainly incomplete arc structures that follow the same subunit packing arrangements as found in isolation. Both assemblies on membranes use their P2 ß-hairpin for binding to the lipid membrane surface. Overall, these structural snapshots suggest a molecular mechanism for PFN2 pre-pore to pore transition on a targeted membrane, potentially using the twisted pore as an intermediate or alternative state to the flat conformation, with the capacity to cause bilayer distortion during membrane insertion.

Capturing pore-forming intermediates of MACPF and binary toxin assemblies by cryoEM.

Deployed by both pathogenic bacteria and host immune systems, pore-forming proteins rupture target membranes and can serve as conduits for effector proteins. Understanding how these proteins work relies on capturing assembly intermediates. Advances in cryoEM allowing in silico purification of heterogeneous assemblies has led to new insights into two main classes of pore-forming proteins: membrane attack complex perforin (MACPF) proteins and binary toxins. The structure of an immune activation complex, sMAC, shows how pores form by sequential templating and insertion of ß-hairpins. CryoEM structures of bacterial binary toxins present a series of transitions along the pore formation pathway and reveal a general mechanism of effector protein translocation. Future developments in time-resolved cryoEM could capture and place short-lived states along the trajectory of pore-formation.

Structural, Functional and Computational Studies of Membrane Recognition by Plasmodium Perforin-Like Proteins 1 and 2.

Perforin-like proteins (PLPs) play key roles in mechanisms associated with parasitic disease caused by the apicomplexan parasites Plasmodium and Toxoplasma. The T. gondii PLP1 (TgPLP1) mediates tachyzoite egress from cells, while the five Plasmodium PLPs carry out various roles in the life cycle of the parasite and with respect to the molecular basis of disease. Here we focus on Plasmodium vivax PLP1 and PLP2 (PvPLP1 and PvPLP2) compared to TgPLP1. Determination of the crystal structure of the membrane-binding APCß domain of PvPLP1 reveals notable differences with TgPLP1, reflected in its inability to bind lipid bilayers as TgPLP1 and PvPLP2 do. Molecular dynamics simulations combined with site-directed mutagenesis and functional assays allow dissection of the binding interactions of TgPLP1 and PvPLP2 on lipid bilayers, and reveal similar tropisms for lipids enriched in the inner leaflet of the mammalian plasma membrane. In addition PvPLP2 displays a secondary synergistic interaction side-on from its principal bilayer interface. This study underlines the substantial differences between the biophysical properties of the APCß domains of apicomplexan PLPs, which reflect their significant sequence diversity. Such differences will be important factors in determining the cell targeting and membrane-binding activity of the different proteins in parasitic life cycles and disease.

Single-particle cryo-EM reveals conformational variability of the oligomeric VCC ß-barrel pore in a lipid bilayer.

Vibrio cholerae cytolysin (VCC) is a water-soluble, membrane-damaging, pore-forming toxin (PFT) secreted by pathogenic V. cholerae, which causes eukaryotic cell death by altering the plasma membrane permeability. VCC self-assembles on the cell surface and undergoes a dramatic conformational change from prepore to heptameric pore structure. Over the past few years, several high-resolution structures of detergent-solubilized PFTs have been characterized. However, high-resolution structural characterization of small ß-PFTs in a lipid environment is still rare. Therefore, we used single-particle cryo-EM to characterize the structure of the VCC oligomer in large unilamellar vesicles, which is the first atomic-resolution cryo-EM structure of VCC. From our study, we were able to provide the first documented visualization of the rim domain amino acid residues of VCC interacting with lipid membrane. Furthermore, cryo-EM characterization of lipid bilayer-embedded VCC suggests interesting conformational variabilities, especially in the transmembrane channel, which could have a potential impact on the pore architecture and assist us in understanding the pore formation mechanism.

Immunogenic camptothesome nanovesicles comprising sphingomyelin-derived camptothecin bilayers for safe and synergistic cancer immunochemotherapy.

Despite the enormous therapeutic potential of immune checkpoint blockade (ICB), it benefits only a small subset of patients. Some chemotherapeutics can switch 'immune-cold' tumours to 'immune-hot' to synergize with ICB. However, safe and universal therapeutic platforms implementing such immune effects remain scarce. We demonstrate that sphingomyelin-derived camptothecin nanovesicles (camptothesomes) elicit potent granzyme-B- and perforin-mediated cytotoxic T lymphocyte (CTL) responses, potentiating PD-L1/PD-1 co-blockade to eradicate subcutaneous MC38 adenocarcinoma with developed memory immunity. In addition, camptothesomes improve the pharmacokinetics and lactone stability of camptothecin, avoid systemic toxicities, penetrate deeply into the tumour and outperform the antitumour efficacy of Onivyde. Camptothesome co-load the indoleamine 2,3-dioxygenase inhibitor indoximod into its interior using the lipid-bilayer-crossing capability of the immunogenic cell death inducer doxorubicin, eliminating clinically relevant advanced orthotopic CT26-Luc tumours and late-stage B16-F10-Luc2 melanoma, and achieving complete metastasis remission when combined with ICB and folate targeting. The sphingomyelin-derived nanotherapeutic platform and doxorubicin-enabled transmembrane transporting technology are generalizable to various therapeutics, paving the way for transformation of the cancer immunochemotherapy paradigm.

Automated Electrical Quantification of Vitamin†B1 in a Bodily Fluid using an Engineered Nanopore Sensor.

The ability to measure the concentration of metabolites in biological samples is important, both in the clinic and for home diagnostics. Here we present a nanopore-based biosensor and automated data analysis for quantification of thiamine in urine in less than a minute, without the need for recalibration. For this we use the Cytolysin A nanopore and equip it with an engineered periplasmic thiamine binding protein (TbpA). To allow fast measurements we tuned the affinity of TbpA for thiamine by redesigning the π-π stacking interactions between the thiazole group of thiamine and TbpA. This substitution resulted furthermore in a marked difference between unbound and bound state, allowing the reliable discrimination of thiamine from its two phosphorylated forms by residual current only. Using an array of nanopores, this will allow the quantification within seconds, paving the way for next-generation single-molecule metabolite detection systems.

Cholesterol stimulates the lytic activity of Adenylate Cyclase Toxin on lipid membranes by promoting toxin oligomerization and formation of pores with a greater effective size.

Several toxins acting on animal cells present different, but specific, interactions with cholesterol. Bordetella pertussis infects the human respiratory tract and causes whooping cough, a highly contagious and resurgent disease. Its virulence factor adenylate cyclase toxin (ACT) plays an important role in the course of infection. ACT is a pore-forming cytolysin belonging to the Repeats in ToXin (RTX) family of leukotoxins/hemolysins and is capable of permeabilizing several cell types and lipid vesicles. Previously, we observed that in the presence of cholesterol ACT induces greater liposome permeabilization. Similarly, recent reports also implicate cholesterol in the cytotoxicity of an increasing number of pore-forming RTX toxins. However, the mechanistic details by which this sterol promotes the lytic activity of ACT or of these other RTX toxins remain largely unexplored and poorly understood. Here, we have applied a combination of biophysical techniques to dissect the role of cholesterol in pore formation by ACT. Our results indicate that cholesterol enhances the lytic potency of ACT by promoting toxin oligomerization, a step which is indispensable for ACT to accomplish membrane permeabilization and cell lysis. Since our experimental design eliminates the possibility that this cholesterol effect derives from toxin accumulation due to lateral lipid phase segregation, we hypothesize that cholesterol facilitates lytic pore formation, by favoring a toxin conformation more prone to protein-protein interactions and oligomerization. Our data shed light on the complex relationship between lipid membranes and protein toxins acting on these membranes. Coupling cholesterol binding, increased oligomerization and increased lytic activity is likely pertinent for other RTX cytolysins.

A novel allele of the Arabidopsis thaliana MACPF protein CAD1 results in deregulated immune signaling.

Immune recognition in plants is governed by two major classes of receptors: pattern recognition receptors (PRRs) and nucleotide-binding leucine-rich repeat receptors (NLRs). Located at the cell surface, PRRs bind extracellular ligands originating from microbes (indicative of "non-self") or damaged plant cells (indicative of "infected-self"), and trigger signaling cascades to protect against infection. Located intracellularly, NLRs sense pathogen-induced physiological changes and trigger localized cell death and systemic resistance. Immune responses are under tight regulation in order to maintain homeostasis and promote plant health. In a forward-genetic screen to identify regulators of PRR-mediated immune signaling, we identified a novel allele of the membrane-attack complex and perforin (MACPF)-motif containing protein CONSTITUTIVE ACTIVE DEFENSE 1 (CAD1) resulting from a missense mutation in a conserved N-terminal cysteine. We show that cad1-5 mutants display deregulated immune signaling and symptoms of autoimmunity dependent on the lipase-like protein ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1), suggesting that CAD1 integrity is monitored by the plant immune system. We further demonstrate that CAD1 localizes to both the cytosol and plasma membrane using confocal microscopy and subcellular fractionation. Our results offer new insights into immune homeostasis and provide tools to further decipher the intriguing role of MACPF proteins in plants.

In Vitro Detected hly II Cytotoxin in a Strain of Staphylococcus aureus (BM S-2) and Plant-Derived Aromatic Components: a Molecular Docking Study.

In time, diagnosis and detection of virulence factor and its pathogenomics study continues to grow and this leads to novel treatments for infectious diseases. The objective of this study was to detect and characterise virulence genes in a haemolytic strain of Staphylococcus aureus in vitro and molecular interaction studies with herbal essential oil components in silico. A hospital biosample-isolated strain of Staphylococcus aureus (BMS-2) was resistant towards Cephalosporin. The PCR-amplified FASTA nucleotide sequence was identical with S. aureus strains absolutely. The calculated GC value was 34.05%. The translated protein sequence was identified with a conserved domain of hlyII ß-channel forming cytolysin belonging to leukocidin superfamily and was predicted as a stable, non-transmembrane protein comprising B cell epitopes. Structurally, the protein was found to be composed of α helix, π-helix, extended strands, ß-sheet, turn and bends with atomic composition as C658H1026N174O200S2. The molecular docking studies made between the HlyII cytolysin (receptor) and wet lab studied essential oil components (citral a, citronellol, eucalyptol, eugenol, geraniol, linalool, menthol, piperine and thymol) as ligands using Autodock 1.5.6 tool had inferred about prevalence of hydrogen bonds as well as covalent bonds in the intermolecular interactions. Amino acids like Tyr68, Tyr 69, Asn106, Asp67 and Asn106 were observed to be the most active residues for H-bond and hydrophobic bonds respectively. Only geraniol had interaction with glycine residue of the toxin molecule. In conclusion, geraniol with the highest ligand efficiency was observed to be the most potent phyto-constituent interacting with the in vitro detected hlyII cytotoxin.

Preparation of Cytolysin A (ClyA) Nanopores.

The ionic currents passing through nanopores can be used to sequence DNA and identify molecules at the single-molecule level. Recently, researchers have started using nanopores for the detection and analysis of proteins, providing a new platform for single-molecule enzymology studies and more efficient biomolecular sensing applications. For this approach, the homo-oligomeric Cytolysin A (ClyA) nanopore has been demonstrated as a powerful tool. Here, we describe a simple protocol allowing the production of ClyA nanopores. Monomers of ClyA are expressed in Escherichia coli and oligomerized in the presence of detergent. Subsequently, different oligomer variants are electrophoretically resolved and stored in a gel matrix for long-term use.

Mechanistic Insights into Pore Formation by an α-Pore Forming Toxin: Protein and Lipid Bilayer Interactions of Cytolysin A.

Pore forming toxins (PFTs) are the largest class of bacterial toxins playing a central role in bacterial pathogenesis. They are proteins specifically designed to form nanochannels in the membranes of target cells, ultimately resulting in cell death and establishing infection. PFTs are broadly classified as α- and ß-PFTs, depending on secondary structures that form the transmembrane channel. A unique feature about this class of proteins is the drastic conformational changes and complex oligomerization pathways that occur upon exposure to the plasma membrane. A molecular understanding of pore formation has implications in designing novel intervention strategies to combat rising antimicrobial resistance, targeted-cancer therapy, as well as designing nanopores for specialized technologies. Central to unraveling the pore formation pathway is the availability of high resolution crystal structures. In this regard, ß-toxins are better understood, when compared with α-toxins whose pore forming mechanisms are complicated by an incomplete knowledge of the driving forces for amphiphatic membrane-inserted helices to organize into functional pores. With the publication of the first crystal structure for an α-toxin, cytolysin A (ClyA), in 2009 we embarked on an extensive multiscale study to unravel its pore forming mechanism. This Account represents the collective mechanistic knowledge gained in our laboratories using a variety of experimental and theoretical techniques which include large scale molecular dynamics (MD) simulations, kinetic modeling studies, single-molecule fluorescence imaging, and super-resolution spectroscopy. We reported MD simulations of the ClyA protomer, oligomeric intermediates, and full pore complex in a lipid bilayer and mapped the conformational transitions that accompany membrane binding. Using single-molecule fluorescence imaging, the conformational transition was experimentally verified by analysis of various diffusion states of membrane bound ClyA. Importantly, we have uncovered a hitherto unknown putative cholesterol binding motif in the membrane-inserted helix of ClyA. Distinct binding pockets for cholesterol formed by adjacent membrane-inserted helices are revealed in MD simulations. Cholesterol appears to play a dual role by stabilizing both the membrane-inserted protomer as well as oligomeric intermediates. Molecular dynamics simulations and kinetic modeling studies suggest that the membrane-inserted arcs oligomerize reversibly to form the predominant transmembrane oligomeric intermediates during pore formation. We posit that this mechanistic understanding of the complex action of α-PFTs has implications in unraveling pore assembly across the wider family of bacterial toxins. With emerging antimicrobial resistance, alternate therapies may rely on disrupting pore functionality or oligomerization of these pathogenic determinants utilized by bacteria, and our study includes assessing the potential for dendrimers as pore blockers.

Tyrosine in the hinge region of the pore-forming motif regulates oligomeric ß-barrel pore formation by Vibrio cholerae cytolysin.

ß-barrel pore-forming toxins perforate cell membranes by forming oligomeric ß-barrel pores. The most crucial step is the membrane-insertion of the pore-forming motifs that create the transmembrane ß-barrel scaffold. Molecular mechanism that regulates structural reorganization of these pore-forming motifs during ß-barrel pore-formation still remains elusive. Using Vibrio cholerae cytolysin as an archetypical example of the ß-barrel pore-forming toxin, we show that a key tyrosine residue (Y321) in the hinge region of the pore-forming motif plays crucial role in this process. Mutation of Y321 abrogates oligomerization of the membrane-bound toxin protomers, and blocks subsequent steps of pore-formation. Our study suggests that the presence of Y321 in the hinge region of the pore-forming motif is crucial for the toxin molecule to sense membrane-binding, and to trigger essential structural rearrangements required for the subsequent oligomerization and pore-formation process. Such a regulatory mechanism of pore-formation by V. cholerae cytolysin has not been documented earlier in the structurally related ß-barrel pore-forming toxins.

Exaptation of two ancient immune proteins into a new dimeric pore-forming toxin in snails.

The Membrane Attack Complex-Perforin (MACPF) family is ubiquitously found in all kingdoms. They have diverse cellular roles, however MACPFs with pore-forming toxic function in venoms and poisons are very rare in animals. Here we present the structure of PmPV2, a MACPF toxin from the poisonous apple snail eggs, that can affect the digestive and nervous systems of potential predators. We report the three-dimensional structure of PmPV2, at 17.2 Å resolution determined by negative-stain electron microscopy and its solution structure by small angle X-ray scattering (SAXS). We found that PV2s differ from nearly all MACPFs in two respects: it is a dimer in solution and protomers combine two immune proteins into an AB toxin. The MACPF chain is linked by a single disulfide bond to a tachylectin chain, and two heterodimers are arranged head-to-tail by non-covalent forces in the native protein. MACPF domain is fused with a putative new Ct-accessory domain exclusive to invertebrates. The tachylectin is a six-bladed ß-propeller, similar to animal tectonins. We experimentally validated the predicted functions of both subunits and demonstrated for the first time that PV2s are true pore-forming toxins. The tachylectin "B" delivery subunit would bind to target membranes, and then the MACPF "A" toxic subunit would disrupt lipid bilayers forming large pores altering the plasma membrane conductance. These results indicate that PV2s toxicity evolved by linking two immune proteins where their combined preexisting functions gave rise to a new toxic entity with a novel role in defense against predation. This structure is an unparalleled example of protein exaptation.

Engineering and Modeling the Electrophoretic Trapping of a Single Protein Inside a Nanopore.

The ability to confine and to study single molecules has enabled important advances in natural and applied sciences. Recently, we have shown that unlabeled proteins can be confined inside the biological nanopore Cytolysin A (ClyA) and conformational changes monitored by ionic current recordings. However, trapping small proteins remains a challenge. Here, we describe a system where steric, electrostatic, electrophoretic, and electro-osmotic forces are exploited to immobilize a small protein, dihydrofolate reductase (DHFR), inside ClyA. Assisted by electrostatic simulations, we show that the dwell time of DHFR inside ClyA can be increased by orders of magnitude (from milliseconds to seconds) by manipulation of the DHFR charge distribution. Further, we describe a physical model that includes a double energy barrier and the main electrophoretic components for trapping DHFR inside the nanopore. Simultaneous fits to the voltage dependence of the dwell times allowed direct estimates of the cis and trans translocation probabilities, the mean dwell time, and the force exerted by the electro-osmotic flow on the protein (≅9 pN at -50 mV) to be retrieved. The observed binding of NADPH to the trapped DHFR molecules suggested that the engineered proteins remained folded and functional inside ClyA. Contact-free confinement of single proteins inside nanopores can be employed for the manipulation and localized delivery of individual proteins and will have further applications in single-molecule analyte sensing and enzymology studies.

Structure-function characterization of an insecticidal protein GNIP1Aa, a member of an MACPF and ß-tripod families.

The crystal structure of the Gram-negative insecticidal protein, GNIP1Aa, has been solved at 2.5-Å resolution. The protein consists of two structurally distinct domains, a MACPF (membrane attack complex/PerForin) and a previously uncharacterized type of domain. GNIP1Aa is unique in being a prokaryotic MACPF member to have both its structure and function identified. It was isolated from a Chromobacterium piscinae strain and is specifically toxic to Diabrotica virgifera virgifera larvae upon feeding. In members of the MACPF family, the MACPF domain has been shown to be important for protein oligomerization and formation of transmembrane pores, while accompanying domains define the specificity of the target of the toxicity. In GNIP1Aa the accompanying C-terminal domain has a unique fold composed of three pseudosymmetric subdomains with shared sequence similarity, a feature not obvious from the initial sequence examination. Our analysis places this domain into a protein family, named here ß-tripod. Using mutagenesis, we identified functionally important regions in the ß-tripod domain, which may be involved in target recognition.

Structural basis of Toxoplasma gondii perforin-like protein 1 membrane interaction and activity during egress.

Intracellular pathogens must egress from the host cell to continue their infectious cycle. Apicomplexans are a phylum of intracellular protozoans that have evolved members of the membrane attack complex and perforin (MACPF) family of pore forming proteins to disrupt cellular membranes for traversing cells during tissue migration or egress from a replicative vacuole following intracellular reproduction. Previous work showed that the apicomplexan Toxoplasma gondii secretes a perforin-like protein (TgPLP1) that contains a C-terminal Domain (CTD) which is necessary for efficient parasite egress. However, the structural basis for CTD membrane binding and egress competency remained unknown. Here, we present evidence that TgPLP1 CTD prefers binding lipids that are abundant in the inner leaflet of the lipid bilayer. Additionally, solving the high-resolution crystal structure of the TgPLP1 APCß domain within the CTD reveals an unusual double-layered ß-prism fold that resembles only one other protein of known structure. Three direct repeat sequences comprise subdomains, with each constituting a wall of the ß-prism fold. One subdomain features a protruding hydrophobic loop with an exposed tryptophan at its tip. Spectrophotometric measurements of intrinsic tryptophan fluorescence are consistent with insertion of the hydrophobic loop into a target membrane. Using CRISPR/Cas9 gene editing we show that parasite strains bearing mutations in the hydrophobic loop, including alanine substitution of the tip tryptophan, are equally deficient in egress as a strain lacking TgPLP1 altogether. Taken together our findings suggest a crucial role for the hydrophobic loop in anchoring TgPLP1 to the membrane to support its cytolytic activity and egress function.

Molecular characterization of three novel perforins in common carp (Cyprinus carpio L.) and their expression patterns during larvae ontogeny and in response to immune challenges.

BACKGROUND: In the host immune system, perforin is a cytotoxic effector molecule that eliminate virus-infected and malignant cells. Moreover, some recent studies also imply the involvement of perforin in antibacterial immunity. Common carp (Cyprinus carpio L.), one of the most economically important fish species in China, has a high susceptibility to viruses and bacteria. Thus far, in common carp, no data are available regarding the identification and immunologic function of the perforin. RESULTS: In the present study, the cDNA and genomic DNA sequences of three perforin isoform genes were cloned and characterized in common carp, named CcPRF1, CcPRF2 and CcPRF3. Amino acid sequences of the three CcPRFs were quite different, with identities ranged from 37.3 to 39.5%. Phylogenetic analysis showed that three CcPRFs, each in a separate sub-branch, possessed closer evolutionary relationship with other teleost perforins, especially with cyprinid fishes, than higher vertebrates. Expression analysis revealed that each CcPRF gene was differentially expressed in all of the nine tested tissues. During larvae ontogeny, each CcPRF displayed a distinct expression pattern, while with a common expression peak at 22 days post hatching (dph). Moreover, in vivo or in vitro, after stimulation with polyI:C, LPS and Aeromonas hydrophila, each CcPRF was induced significantly, with differential expression dynamics. CONCLUSIONS: Our findings suggest that perforin might play significant roles in larval immune system and in the immune defense of common carp against viral and bacterial pathogens. Meantime, the differential expression dynamics seem to imply possible different cellular locations or functional differences across various CcPRF isoforms.

Protein Motion and Configurations in a Form-Fitting Nanopore: Avidin in ClyA.

We probe the molecular dynamics and states of an avidin protein as it is captured and trapped in a voltage-biased cytolysin A nanopore using time-resolved single-molecule electrical conductance signals. The data for very large numbers of single-molecule events are analyzed and presented by a new method that provides clear visual insight into the molecular scale processes. Avidin in cytolysin A has surprisingly rich conductance spectra that reveal transient and more permanently trapped protein configurations in the pore and how they evolve into one another. We identify a long-lasting, stable, and low-noise configuration of avidin in the nanopore into which avidin can be reliably trapped and released. This may prove useful for single-molecule studies of other proteins that can be biotinylated and then transported by avidin to the pore via their coupling to avidin with biotin-avidin linking. We demonstrate the sensitivity of this system with detection of biotin attached to avidin captured by the pore.

A mouse model reproducing the pathophysiology of neonatal group B streptococcal infection.

Group B streptococcal (GBS) meningitis remains a devastating disease. The absence of an animal model reproducing the natural infectious process has limited our understanding of the disease and, consequently, delayed the development of effective treatments. We describe here a mouse model in which bacteria are transmitted to the offspring from vaginally colonised pregnant females, the natural route of infection. We show that GBS strain BM110, belonging to the CC17 clonal complex, is more virulent in this vertical transmission model than the isogenic mutant BM110∆cylE, which is deprived of hemolysin/cytolysin. Pups exposed to the more virulent strain exhibit higher mortality rates and lung inflammation than those exposed to the attenuated strain. Moreover, pups that survive to BM110 infection present neurological developmental disability, revealed by impaired learning performance and memory in adulthood. The use of this new mouse model, that reproduces key steps of GBS infection in newborns, will promote a better understanding of the physiopathology of GBS-induced meningitis.

Structures of monomeric and oligomeric forms of the Toxoplasma gondii perforin-like protein 1.

Toxoplasma and Plasmodium are the parasitic agents of toxoplasmosis and malaria, respectively, and use perforin-like proteins (PLPs) to invade host organisms and complete their life cycles. The Toxoplasma gondii PLP1 (TgPLP1) is required for efficient exit from parasitophorous vacuoles in which proliferation occurs. We report structures of the membrane attack complex/perforin (MACPF) and Apicomplexan PLP C-terminal ß-pleated sheet (APCß) domains of TgPLP1. The MACPF domain forms hexameric assemblies, with ring and helix geometries, and the APCß domain has a novel ß-prism fold joined to the MACPF domain by a short linker. Molecular dynamics simulations suggest that the helical MACPF oligomer preserves a biologically important interface, whereas the APCß domain binds preferentially through a hydrophobic loop to membrane phosphatidylethanolamine, enhanced by the additional presence of inositol phosphate lipids. This mode of membrane binding is supported by site-directed mutagenesis data from a liposome-based assay. Together, these structural and biophysical findings provide insights into the molecular mechanism of membrane targeting by TgPLP1.