1kd6
Solution structure of the eukaryotic pore-forming cytolysin equinatoxin II
Structural highlights
FunctionACTP2_ACTEQ Pore-forming protein that forms cations-selective hydrophilic pores of around 1 nm and causes cardiac stimulation and hemolysis. Pore formation is a multi-step process that involves specific recognition of membrane sphingomyelin (but neither cholesterol nor phosphatidylcholine) using aromatic rich region and adjacent phosphocholine (POC) binding site, firm binding to the membrane (mainly driven by hydrophobic interactions) accompanied by the transfer of the N-terminal region to the lipid-water interface and finally pore formation after oligomerization of several monomers. Cytolytic effects include red blood cells hemolysis, platelet aggregation and lysis, cytotoxic and cytostatic effects on fibroblasts. Lethality in mammals has been ascribed to severe vasospasm of coronary vessels, cardiac arrhythmia, and inotropic effects. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedSea anemones produce a family of 18-20 kDa proteins, the actinoporins, that lyse cells by forming pores in cell membranes. Sphingomyelin plays an important role in their lytic activity, with membranes lacking this lipid being largely refractory to these toxins. The structure of the actinoporin equinatoxin II in aqueous solution, determined from NMR data, consists of two short helices packed against opposite faces of a beta-sandwich structure formed by two five-stranded beta-sheets. The protein core has extensive hydrophobic interfaces formed by residues projecting from the internal faces of the two beta-sheets. 15N relaxation data show uniform backbone dynamics, implying that equinatoxin II in solution is relatively rigid, except at the N terminus; its inferred rotational correlation time is consistent with values for monomeric proteins of similar mass. Backbone amide exchange rate data also support the view of a stable structure, even though equinatoxin II lacks disulfide bonds. As monitored by NMR, it unfolds at around 70 degrees C at pH 5.5. At 25 degrees C the structure is stable over the pH range 2.5-7.3 but below pH 2.5 it undergoes a slow transition to an incompletely unfolded structure resembling a molten globule. Equinatoxin II has two significant patches of positive electrostatic potential formed by surface-exposed Lys and Arg residues, which may assist its interaction with charged regions of the lipid head groups. Tyr and Trp residues on the surface may also contribute by interacting with the carbonyl groups of the acyl chains of target membranes. Data from mutational studies and truncated analogues identify two regions of the protein involved in membrane interactions, the N-terminal helix and the Trp-rich region. Once the protein is anchored, the N-terminal helix may penetrate the membrane, with up to four helices lining the pore, although other mechanisms of pore formation cannot be ruled out. Solution structure of the eukaryotic pore-forming cytolysin equinatoxin II: implications for pore formation.,Hinds MG, Zhang W, Anderluh G, Hansen PE, Norton RS J Mol Biol. 2002 Feb 1;315(5):1219-29. PMID:11827489[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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