1qmd
From Proteopedia
calcium bound closed form alpha-toxin from Clostridium perfringens
Structural highlights
FunctionPHLC_CLOP1 Bacterial hemolysins are exotoxins that attack blood cell membranes and cause cell rupture. Constitutes an essential virulence factor in gas gangrene. Binds to eukaryotic membranes where it hydrolyzes both phosphatidylcholine and sphingomyelin. The diacylglycerol produced can activate both the arachidonic acid pathway, leading to modulation of the inflammatory response cascade and thrombosis, and protein kinase C, leading to activation of eukaryotic phospholipases and further membrane damage. Acts on human and mouse erythrocytes, but not on rabbit or horse erythrocytes. 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 PubMedAlpha-toxin is the key determinant in gas-gangrene. The toxin, a phospholipase C, cleaves phosphatidylcholine in eukaryotic cell membranes. Calcium ions have been shown to be required for the specific binding of toxin to membranes prior to phospholipid cleavage. Reported X-ray crystallographic structures of the toxin show that the C-terminal domain has a fold that is analogous to the eukaryotic calcium and membrane-binding C2 domains. We report the binding sites for three calcium ions that have been identified, by crystallographic methods, in the C-terminal domain of the protein close to the postulated membrane-binding surface. The position of these ions at the tip of the domain, and their function (to facilitate membrane binding) is similar to that of calcium ions observed bound to C2 domains. Using the optical spectroscopic techniques of circular dichroism (CD) and fluorescence spectroscopy, pronounced changes to both near and far-UV CD and tryptophan emission fluorescence upon addition of calcium to the C-terminal domain of alpha-toxin have been observed. The changes in near-UV CD, fluorescence enhancement and a 2 nm blue-shift in the fluorescence emission spectrum are consistent with tryptophan residue(s) becoming more immobilised in a hydrophobic environment. Calcium binding appears to be low-affinity: Kd approximately 175-250 microM at pH 8 assuming a 1:1 stoichiometry. as measured by spectroscopic methods. Characterisation of the calcium-binding C-terminal domain of Clostridium perfringens alpha-toxin.,Naylor CE, Jepson M, Crane DT, Titball RW, Miller J, Basak AK, Bolgiano B J Mol Biol. 1999 Dec 3;294(3):757-70. PMID:10610794[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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