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44-553: Archetypal members of the family are complement C9 and perforin , both of which function in human immunity . C9 functions by punching holes in the membranes of Gram-negative bacteria. Perforin is released by cytotoxic T cells and lyses virally infected and transformed cells. In addition, perforin permits delivery of cytotoxic proteases called granzymes that cause cell death . Deficiency of either protein can result in human disease. Structural studies reveal that MACPF domains are related to cholesterol-dependent cytolysins (CDCs),

88-499: A 16-strand 'stalk'. The Panton-Valentine leucocidin S structure (PDB: 1T5R) shows a highly related structure, but in its soluble monomeric state. This shows that the strands involved in forming the 'stalk' are in a very different conformation – shown in Fig 2. While the Bin toxin of Lysinibacillus sphaericus is able to form pores in artificial membranes and mosquito cells in culture, it also causes

132-538: A MACPF protein, however, this molecule appears non-lytic. The X-ray crystal structure of Plu-MACPF, a protein from the insect pathogenic enterobacteria Photorhabdus luminescens has been determined (figure 1). [5] These data reveal that the MACPF domain is homologous to pore forming cholesterol dependent cytolysins (CDC's) from gram-positive pathogenic bacteria such as Clostridium perfringens (which causes gas gangrene ). The amino acid sequence identity between

176-406: A bacterial MACPF protein, Plu-MACPF from Photorhabdus luminescens was determined ( PDB : 2QP2 ​). The MACPF domain is structurally similar to pore-forming cholesterol-dependent cytolysins from gram-positive bacteria , suggesting that MACPF proteins create pores and disrupt cell membranes similar to cytolysin. A representative list of proteins belonging to the MACPF family can be found in

220-484: A cell can cause the cell to swell up uncontrollably: this causes a process called blebbing , wherein large parts of the cell membrane are distorted and give way under the mounting internal pressure. In the end, this can cause the cell to burst. In particular, nuclear - free erythrocytes under the influence of alpha-staphylotoxin undergo hemolysis with the loss of a large protein hemoglobin. There are many different types of binary toxins. The term binary toxin simply implies

264-435: A cell is disrupted. Ions and small molecules, such as amino acids and nucleotides within the cell, flow out, and water from the surrounding tissue enters. The loss of important small molecules to the cell can disrupt protein synthesis and other crucial cellular reactions. The loss of ions, especially calcium , can cause cell signaling pathways to be spuriously activated or deactivated. The uncontrolled entry of water into

308-549: A conformational change in which a group of α-helices in each monomer change into extended, amphipathic β-hairpins that span the membrane, in a manner reminiscent of α-haemolysin, albeit on a much larger scale (Fig 3). CDCs are homologous to the MACPF family of pore-forming toxins, and it is suggested that both families use a common mechanism (Fig 4). Eukaryote MACPF proteins function in immune defence and are found in proteins such as perforin and complement C9 though perivitellin-2

352-443: A family of pore forming toxins previously thought to only exist in bacteria. As of early 2016, there are three families belonging to the MACPF superfamily: Proteins containing MACPF domains play key roles in vertebrate immunity, embryonic development, and neural-cell migration. The ninth component of complement and perforin form oligomeric pores that lyse bacteria and kill virus-infected cells, respectively. The crystal structure of

396-623: A large pore that punches a hole in the outer membrane of gram-negative bacteria . Perforin is stored in granules within cytotoxic T-cells and is responsible for killing virally infected and transformed cells. Perforin functions via two distinct mechanisms. Firstly, like C9, high concentrations of perforin can form pores that lyse cells. Secondly, perforin permits delivery of the cytotoxic granzymes A and B into target cells. Once delivered, granzymes are able to induce apoptosis and cause target cell death. The plant protein CAD1 ( TC# 1.C.39.11.3 ) functions in

440-495: A limited range of target insects, making them safe biological control agents. Insecticidal members of the Etx/Mtx2 family include Mtx2 and Mtx3 from Lysinibacillus sphaericus that can control mosquito vectors of human diseases and also Cry15, Cry23, Cry33, Cry38, Cry45, Cry51, Cry60, Cry64 and Cry74 from Bacillus thuringiensis that control a range of insect pests that can cause great losses to agriculture. Insecticidal toxins in

484-478: A number of families including Leukocidins, Etx-Mtx2, Toxin-10, and aegerolysin. X-ray crystallographic structures have revealed some commonalities: α-hemolysin and Panton-Valentine leukocidin S are structurally related. Similarly, aerolysin and Clostridial Epsilon-toxin. and Mtx2 are linked in the Etx/Mtx2 family. The ß-PFTs include a number of toxins of commercial interest for the control of pest insects. These toxins are potent but also highly specific to

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528-751: A number of protein exotoxins but may also be produced by other organisms such as apple snails that produce perivitellin-2 or earthworms , who produce lysenin . They are frequently cytotoxic (i.e., they kill cells ), as they create unregulated pores in the membrane of targeted cells. PFTs can be divided into two categories, depending on the alpha-helical or beta-barrel architecture of their transmembrane channel that can consist either of Other categories: According to TCDB , there are following families of pore-forming toxins: β-PFTs are so-named because of their structural characteristics: they are composed mostly of β-strand -based domains. They have divergent sequences, and are classified by Pfam into

572-684: A ribosyl-ADP moiety to surface arginine residue 177 of G-actin. This prevents G-actin assembling to form F-actin, and, thus, the cytoskeleton breaks down, resulting in cell death. Insecticidal members of the ADP-ribosyltransferase family of toxins include the Mtx1 toxin of Lysinibacillus sphaericus and the Vip1/Vip2 toxin of Bacillus thuringiensis and some members of the toxin complex (Tc) toxins from gram negative bacteria such as Photorhabdus and Xenorhabdus species. The beta sheet-rich regions of

616-428: A series of other cellular changes including the uptake of toxin in recycling endosomes and the production of large, autophagic vesicles and the ultimate cause of cell death may be apoptotic. Similar effects on cell biology are also seen with other Toxin_10 activities but the roles of these events in toxicity remain to be established. The transition between soluble monomer and membrane-associated protomer to oligomer

660-499: A two part toxin where both components are necessary for toxic activity. Several β-PFTs form binary toxins. As discussed above, the majority of the Toxin_10 family proteins act as part of binary toxins with partner proteins that may belong to the Toxin_10 or other structural families. The interplay of the individual components has not been well studied to date. Other beta sheet toxins of commercial importance are also binary. These include

704-399: Is a MACPF protein involved in the complement system , which is part of the innate immune system . Once activated, about 12-18 molecules of C9 polymerize to form pores in target cell membranes , causing lysis and cell death. C9 is one member of the complement membrane attack complex (MAC), which also includes complement components C5b , C6 , C7 and C8 .   The formation of

748-411: Is a MACPF attached to a delivery lectin that has enterotoxic and neurotoxic properties toward mice. A family of highly conserved cholesterol-dependent cytolysins, closely related to perfringolysin from Clostridium perfringens are produced by bacteria from across the order Bacillales and include anthrolysin, alveolysin and sphaericolysin. Sphaericolysin has been shown to exhibit toxicity to

792-415: Is involved in membrane interactions and entry of the enzymatic component into the cell. The membrane interacting component may have structural domains that are rich in beta sheets. Binary toxins, such as anthrax lethal and edema toxins (Main article: Anthrax toxin), C. perfringens iota toxin and C. difficile cyto-lethal toxins consist of two components (hence binary ): In these enzymatic binary toxins,

836-541: Is involved in sea urchin ( Heliocidaris erythrogramma ) development. Drosophila Torso-like protein ( TC# 1.C.39.15.1 ), which controls embryonic patterning, also contains a MACPF domain. Its function is implicated in a receptor tyrosine kinase signaling pathway that specifies differentiation and terminal cell fate. Functionally uncharacterised MACPF proteins are sporadically distributed in bacteria. Several species of Chlamydia contain MACPF proteins. The insect pathogenic bacteria Photorhabdus luminescens also contains

880-478: Is not a trivial one: It is believed that β-PFTs, follow as similar assembly pathway as the CDCs (see Cholesterol-dependent cytolysins later), in that they must first assemble on the cell-surface (in a receptor-mediated fashion in some cases ) in a pre-pore state. Following this, the large-scale conformational change occurs in which the membrane spanning section is formed and inserted into the membrane. The portion entering

924-454: Is postulated that the green section in PVL 'flips out' to the 'red' conformation as seen in α-Haemolysin. (PDB: 7AHL, 1T5R) β-PFTs are dimorphic proteins that exist as soluble monomers and then assemble to form multimeric assemblies that constitute the pore. Figure 1 shows the pore-form of α-Hemolysin, the first crystal structure of a β-PFT in its pore-form. 7 α-Hemolysin monomers come together to create

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968-587: Is triggered. Anthrax toxin edema toxin triggers a calcium ion influx into the target cell. This subsequently elevates intracellular cAMP levels. This can profoundly alter any sort of immune response, by inhibiting leucocyte proliferation, phagocytosis , and pro inflammatory cytokine release. CDCs , such as pneumolysin, from S. pneumoniae , form pores as large as 260Å (26 nm), containing between 30 and 44 monomer units. Electron microscopy studies of pneumolysin show that it assembles into large multimeric peripheral membrane complexes before undergoing

1012-574: The Vibrio cholerae cytolysin in the pore form is also heptameric; however, Staphylococcus aureus gamma-hemolysin reveals an octomeric pore, consequently with a 16-strand 'stalk'. The Panton-Valentine leucocidin S structure shows a highly related structure, but in its soluble monomeric state. This shows that the strands involved in forming the 'stalk' are in a very different conformation – shown in Fig 2. Structural comparison of pore-form α-Hemolysin (pink/red) and soluble-form PVL (pale green/green). It

1056-451: The B component facilitates the entry of the enzymatic 'payload' (A subunit) into the target cell, by forming homooligomeric pores, as shown above for βPFTs. The A component then enters the cytosol and inhibits normal cell functions by one of the following means: ADP-ribosylation is a common enzymatic method used by different bacterial toxins from various species. Toxins such as C. perfringens iota toxin and C. botulinum C2 toxin, attach

1100-579: The Transporter Classification Database . Many proteins belonging to the MACPF superfamily play key roles in plant and animal immunity. Complement proteins C6-C9 all contain a MACPF domain and assemble into the membrane attack complex. C6, C7 and C8β appear to be non-lytic and function as scaffold proteins within the MAC. In contrast both C8α and C9 are capable of lysing cells. The final stage of MAC formation involves polymerisation of C9 into

1144-408: The lipocalin family and interacts with C8α. The binding site on C8α is known, however, the precise role of C8γ in the MAC remains to be understood. Deficiency of C9, or other components of the MAC results in an increased susceptibility to diseases caused by gram-negative bacteria such as meningococcal meningitis . Overactivity of MACPF proteins can also cause disease. Most notably, deficiency of

1188-545: The membrane of the target cell. Like CDC's MACPF proteins are thus β-pore forming toxins that act like a molecular hole punch. Other crystal structures for members of the MACPF superfamily can be found in RCSB: i.e., 3KK7 ​, 3QOS ​, 3QQH ​, 3RD7 ​, 3OJY ​ Complement regulatory proteins such as CD59 function as MAC inhibitors and prevent inappropriate activity of complement against self cells (Figure 3). Biochemical studies have revealed

1232-521: The Cry23/Cry37 toxin from Bacillus thuringiensis. These toxins have some structural similarity to the Cry34/Cry35 binary toxin but neither component shows a match to established Pfam families and the features of the larger Cry23 protein have more in common with the Etx/Mtx2 family than the Toxin_10 family to which Cry35 belongs. Some binary toxins are composed of an enzymatic component and a component that

1276-891: The MAC inhibitor CD59 results in an overactivity of complement and Paroxysmal nocturnal hemoglobinuria . Perforin deficiency results in the commonly fatal disorder familial hemophagocytic lymphohistiocytosis (FHL or HLH). This disease is characterised by an overactivation of lymphocytes which results in cytokine mediated organ damage. The MACPF protein DBCCR1 may function as a tumor suppressor in bladder cancer . C6 ; C7 ; C8A ; C8B ; C9 ; FAM5B ; FAM5C ; MPEG1 ; PRF1 Complement component 9 5FMW 735 12279 ENSG00000113600 ENSMUSG00000022149 P02748 P06683 NM_001737 NM_013485 NM_001368420 NM_001368421 NP_001728 NP_038513 NP_001355349 NP_001355350 Complement component 9 ( C9 )

1320-488: The MAC occurs through three distinct pathways: the classical, alternative, and lectin pathways. Pore formation by C9 is an important way that bacterial cells are killed during an infection, and the target cell is often covered in multiple MACs. The clinical impact of a deficiency in C9 is an infection with the gram-negative bacterium Neisseria meningitidis . C9 genes include 11 exons and 10 introns when found in fish. In fish,

1364-427: The Mtx1 protein are lectin -like sequences that may be involved in glycolipid interactions. The A component of anthrax toxin lethal toxin is zinc -metallo protease , which shows specificity for a conserved family of mitogen-activated protein kinases . The loss of these proteins results in a breakdown of cell signaling, which, in turn, renders the cell insensitive to outside stimuli – therefore no immune response

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1408-513: The Toxin–10 family show an overall similarity to the aerolysin and Etx/Mtx2 toxin structures but differ in two notable features. While all of these toxins feature a head domain and a larger, extended beta-sheet tail domain, in the Toxin_10 family, the head is formed exclusively from the N-terminal region of the primary amino acid sequence whereas regions from throughout the protein sequence contribute to

1452-426: The head domain in Etx/Mtx2 toxins. In addition, the head domains of the Toxin_10 proteins show lectin-like features of carbohydrate binding domains. The only reported natural targets of Toxin_10 proteins are insects. With the exception of Cry36 and Cry78, the Toxin_10 toxins appear to act as two-part, binary toxins. The partner proteins in these combinations may belong to different structural groups, depending on

1496-768: The individual toxin: two Toxin_10 proteins (BinA and BinB) act together in the Bin mosquitocidal toxin of Lysinibacillus sphaericus; the Toxin_10 Cry49 is co-dependent on the 3-domain toxin family member Cry48 for its activity against Culex mosquito larvae; and the Bacillus thuringiensis Toxin_10 protein Cry35 interacts with the aegerolysin family Cry34 to kill Western Corn Rootworm . This toxin pair has been included in insect resistant plants such as SmartStax corn . β-PFTs are dimorphic proteins that exist as soluble monomers and then assemble to form multimeric assemblies that constitute

1540-406: The liver is the site where the majority of complement components are produced and expressed, but C9 can also be found in other tissues. It is a single-chain glycoprotein with a four domain structure arranged in a globular bundle. MAC formation starts with the assembly of a tetrameric complex with the complement components C6, C7, C8, and C5b. The final step of MAC on target cell surfaces involves

1584-551: The local concentration of the toxins, allowing oligomerisation and pore formation. The BinB Toxin_10 component of the Lysinibacillus sphaericus Bin toxin specifically recognises a GPI anchored alpha glycosidase in the midgut of Culex and Anopheles mosquitoes but not the related protein found in Aedes mosquitoes, hence conferring specificity on the toxin. When the pore is formed, the tight regulation of what can and cannot enter/leave

1628-413: The membrane, referred to as the head, is usually apolar and hydrophobic, this produces an energetically favorable insertion of the pore-forming toxin. Some β-PFTs such as clostridial ε-toxin and Clostridium perfringens enterotoxin (CPE) bind to the cell membrane via specific receptors – possibly certain claudins for CPE, possibly GPI anchors or other sugars for ε-toxin – these receptors help raise

1672-576: The mushroom-shaped pore. The 'cap' of the mushroom sits on the surface of the cell, and the 'stalk' of the mushroom penetrates the cell membrane, rendering it permeable (see later). The 'stalk' is composed of a 14-strand β-barrel, with two strands donated from each monomer. A structure of the Vibrio cholerae cytolysin PDB:3O44 in the pore form is also heptameric; however, Staphylococcus aureus gamma-hemolysin (PDB:3B07) reveals an octomeric pore, consequently with

1716-460: The peptide sequences in C8α and C9 that bind to CD59. Analysis of the MACPF domain structures reveals that these sequences map to the second cluster of helices that unfurl to span the membrane. It is therefore suggested that CD59 directly inhibits the MAC by interfering with conformational change in one of the membrane spanning regions. Other proteins that bind to the MAC include C8γ. This protein belongs to

1760-511: The plant immune response to bacterial infection. The sea anemone Actineria villosa uses a MACPF (AvTX-60A; TC# 1.C.39.10.1 )protein as a lethal toxin. MACPF proteins are also important for the invasion of the Malarial parasite into the mosquito host and the liver. Not all MACPF proteins function in defence or attack. For example, astrotactin-1 ( TC# 9.B.87.3.1 ) is involved in neural cell migration in mammals and apextrin ( TC# 1.C.39.7.4 )

1804-461: The polymerization of C9 molecules bound to C5b8 forming C5b-9. C9 molecules allow cylindrical, asymmetrical transmembrane pores to form. The overall complex belongs to MAC/perforin-like (MACPF)/CDC superfamily. Pore formation involves binding the C9 molecules to the target membrane, membrane molecules forming a pre-pore shape, and conformational change in the TMH1, the first transmembrane region, and TMH2,

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1848-462: The pore. Figure 1 shows the pore-form of α- Hemolysin , the first crystal structure of a β-PFT in its pore-form. 7 α-Hemolysin monomers come together to create the mushroom -shaped pore. The 'cap' of the mushroom sits on the surface of the cell, and the 'stalk' of the mushroom penetrates the cell membrane, rendering it permeable (see later). The 'stalk' is composed of a 14-strand β-barrel , with two strands donated from each monomer. A structure of

1892-491: The second transmembrane region. The formations of pores leads to the killing of foreign pathogens and infected host cells. C9 was found to be the most strongly under expressed serum protein in men who achieved longevity, compared to men who did not. This immunology article is a stub . You can help Misplaced Pages by expanding it . Pore forming toxins Pore-forming proteins ( PFTs , also known as pore-forming toxins ) are usually produced by bacteria , and include

1936-478: The two families is extremely low, and the relationship is not detectable using conventional sequence based data mining techniques. It is suggested that MACPF proteins and CDCs form pores in the same way (figure 1). Specifically it is hypothesised that MACPF proteins oligomerise to form a large circular pore (figure 2). A concerted conformational change within each monomer then results in two α-helical regions unwinding to form four amphipathic β-strands that span

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