Crystal Structure of the Soluble Form of Equinatoxin II, a Pore-Forming Toxin from the Sea Anemone Actinia equina

AbstractBackground: Membrane pore–forming toxins have a remarkable property: they adopt a stable soluble form structure, which, when in contact with a membrane, undergoes a series of transformations, leading to an active, membrane-bound form. In contrast to bacterial toxins, no structure of a pore-forming toxin from an eukaryotic organism has been determined so far, an indication that structural studies of equinatoxin II (EqtII) may unravel a novel mechanism.Results: The crystal structure of the soluble form of EqtII from the sea anemone Actinia equina has been determined at 1.9 Å resolution. EqtII is shown to be a single-domain protein based on a 12 strand β sandwich fold with a hydrophobic core and a pair of α helices, each of which is associated with the face of a β sheet.Conclusions: The structure of the 30 N-terminal residues is the largest segment that can adopt a different structure without disrupting the fold of the β sandwich core. This segment includes a three-turn α helix that lies on the surface of a β sheet and ends in a stretch of three positively charged residues, Lys-30, Arg-31, and Lys-32. On the basis of gathered data, it is suggested that this segment forms the membrane pore, whereas the β sandwich structure remains unaltered and attaches to a membrane as do other structurally related extrinsic membrane proteins or their domains. The use of a structural data site-directed mutagenesis study should reveal the residues involved in membrane pore formation

Interaction of α-Synuclein with Negatively Charged Lipid Membranes Monitored by Surface Plasmon Resonance

Aggregation of presynaptic protein α-synuclein is implicated in the development of Parkinson’s disease. Interaction of α-synuclein with lipid membranes appears to be critical for its physiological and pathological roles. Anionic lipids trigger conformational transition of α-synuclein from its natively disordered into an α-helical structure. Here we used surface plasmon resonance (SPR) to determine the affinities of α-synuclein for the small unilamellar vesicles composed of anionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS) or 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) and neutral 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipids. α-Synuclein bound in a concentration dependent manner to equimolar mixtures of POPC/POPS and POPC/DPPG vesicles. The affinity of α-synuclein for POPC/POPS was ~3-fold higher than for POPC/DPPG. These results indicate that headgroup charge is not the only factor contributing to α-synuclein-membrane association. This work is licensed under a Creative Commons Attribution 4.0 International License

The Coding Region of the Equinatoxin II Gene Lacks Introns

Sea anemones produce several toxic peptides and proteins. Equi- natoxins (Eqt) isolated from the sea anemone Actinia equina are basic cytolytic proteins with molecular masses of approximately 20 kDa. Of the three Eqt purified so far, Eqtll is the most abundant and well characterized. Its gene organization has not yet been studied. In order to obtain the first information about the Eqtll gene structure and sequence, genomic DNA was isolated from A. equina and the target DNA fragment amplified by the polymerase chain reaction (PCR) using three different pairs of oligonucleotide primers deduced from the preserved regions of Eqt cDNA clones. The sequence of the PCR product obtained after amplification of genomic DNA, using an oligonucleotide specific for Eqtll, was almost indistinguishable from that of Eqtll cDNA. As the DNA fragments derived from PCR of genomic DNA were of the same length as those from control PCR reactions performed on an A. equina cDNA library and Eqtll cDNA, the Eqtll gene was proved to be in- tronless, at least within the amplified preproprotein region. The presence of such an intronless gene coding for this cytotoxic protein might be explained by the relative low position of cnidarians in the evolutionary tree or by the advantage provided by a potentially higher rate of gene expression

Pore Formation by Equinatoxin II, a Eukaryotic Protein Toxin, Occurs by Induction of Nonlamellar Lipid Structures

Pore formation in the target cell membranes is a common mechanism used by many toxins in order to kill cells. Among various described mechanisms, a toroidal pore concept was described recently in the course of action of small antimicrobial peptides. Here we provide evidence that such mechanism may be used also by larger toxins. Membrane-destabilizing effects of equinatoxin II, a sea anemone cytolysin, were studied by various biophysical techniques. 31P NMR showed an occurrence of an isotropic component when toxin was added to multilamellar vesicles and heated. This component was not observed with melittin, alpha-staphylococcal toxin, or myoglobin. It does not originate from isolated small lipid structures, since the size of the vesicles after the experiment was similar to the control without toxin. Electron microscopy shows occurrence of a honeycomb structure, previously observed only for some particular lipid mixtures. The analysis of FTIR spectra of the equinatoxin II-lipid complex showed lipid disordering that is consistent with isotropic component observed in NMR. Finally, the cation selectivity of the toxin-induced pores increased in the presence of negatively charged phosphatidic acid, indicating the presence of lipids in the conductive channel. The results are compatible with the toroidal pore concept that might be a general mechanism of pore formation for various membrane-interacting proteins or peptides

Structures of monomeric and oligomeric forms of the Toxoplasma gondiiperforin-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 β-pleated sheet (APCβ) domains of TgPLP1. The MACPF domain forms hexameric assemblies, with ring and helix geometries, and the APCβ domain has a novel β-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 APCβ 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

Archaeal aminoacyl-tRNA synthetases interact with the ribosome to recycle tRNAs

Aminoacyl-tRNA synthetases (aaRS) are essential enzymes catalyzing the formation of aminoacyl-tRNAs, the immediate precursors for encoded peptides in ribosomal protein synthesis. Previous studies have suggested a link between tRNA aminoacylation and high-molecular-weight cellular complexes such as the cytoskeleton or ribosomes. However, the structural basis of these interactions and potential mechanistic implications are not well understood. To biochemically characterize these interactions we have used a system of two interacting archaeal aaRSs: an atypical methanogenic-type seryl-tRNA synthetase and an archaeal ArgRS. More specifically, we have shown by thermophoresis and surface plasmon resonance that these two aaRSs bind to the large ribosomal subunit with micromolar affinities. We have identified the L7/L12 stalk and the proteins located near the stalk base as the main sites for aaRS binding. Finally, we have performed a bioinformatics analysis of synonymous codons in the Methanothermobacter thermautotrophicus genome that supports a mechanism in which the deacylated tRNAs may be recharged by aaRSs bound to the ribosome and reused at the next occurrence of a codon encoding the same amino acid. These results suggest a mechanism of tRNA recycling in which aaRSs associate with the L7/L12 stalk region to recapture the tRNAs released from the preceding ribosome in polysome

pH-triggered endosomal escape of pore-forming Listeriolysin O toxin-coated gold nanoparticles

The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (ERC grant agreement n° 338133)Background: A major bottleneck in drug delivery is the breakdown and degradation of the delivery system through the endosomal/lysosomal network of the host cell, hampering the correct delivery of the drug of interest. In nature, the bacterial pathogen Listeria monocytogenes has developed a strategy to secrete Listeriolysin O (LLO) toxin as a tool to escape the eukaryotic lysosomal system upon infection, allowing it to grow and proliferate unharmed inside the host cell. Results: As a “proof of concept”, we present here the use of purifed His-LLO H311A mutant protein and its conjuga tion on the surface of gold nanoparticles to promote the lysosomal escape of 40 nm-sized nanoparticles in mouse embryonic fbroblasts. Surface immobilization of LLO was achieved after specifc functionalization of the nanoparti cles with nitrile acetic acid, enabling the specifc binding of histidine-tagged proteins. Conclusions: Endosomal acidifcation leads to release of the LLO protein from the nanoparticle surface and its self-assembly into a 300 Å pore that perforates the endosomal/lysosomal membrane, enabling the escape of nanoparticles.Depto. de Química FísicaFac. de Ciencias QuímicasTRUEUnión Europea. FP7Ministerio de Ciencia e Innovación (MICINN)Comunidad de MadridUniversidad Complutense de Madridpu

Structure and mechanism of bactericidal mammalian perforin-2, an ancient agent of innate immunity

Perforin-2 (MPEG1) is thought to enable the killing of invading microbes engulfed by macrophages and other phagocytes, forming pores in their membranes. Loss of perforin-2 renders individual phagocytes and whole organisms significantly more susceptible to bacterial pathogens. Here, we reveal the mechanism of perforin-2 activation and activity using atomic structures of pre-pore and pore assemblies, high-speed atomic force microscopy, and functional assays. Perforin-2 forms a pre-pore assembly in which its pore-forming domain points in the opposite direction to its membrane-targeting domain. Acidification then triggers pore formation, via a 180° conformational change. This novel and unexpected mechanism prevents premature bactericidal attack and may have played a key role in the evolution of all perforin family proteins