1KD6

Solution structure of the eukaryotic pore-forming cytolysin equinatoxin II

Summary for 1KD6

• Entry DOI: 10.2210/pdb1kd6/pdb
• NMR Information: BMRB: 4797
• Descriptor: EQUINATOXIN II (1 entity in total)
• Functional Keywords: cytolysin, pore formation, beta sandwich, toxin, sea anemone, membrane protein
• Biological source: Actinia equina
• Cellular location: Secreted: P61914
• Total number of polymer chains: 1
• Total formula weight: 19859.45

Authors

Hinds, M.G.,Zhang, W.,Anderluh, G.,Hansen, P.E.,Norton, R.S. (deposition date: 2001-11-12, release date: 2002-02-13, Last modification date: 2024-05-22)

Primary citation

Hinds, M.G.,Zhang, W.,Anderluh, G.,Hansen, P.E.,Norton, R.S.
Solution structure of the eukaryotic pore-forming cytolysin equinatoxin II: implications for pore formation.
J.Mol.Biol., 315:1219-1229, 2002

PubMed Abstract: Sea 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.

PubMed: 11827489
DOI: 10.1006/jmbi.2001.5321

Experimental method

SOLUTION NMR