1qm6: Difference between revisions

Alpha-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.

1QM6 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Clostridium_perfringens Clostridium perfringens] with ZN as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/Phospholipase_C Phospholipase C], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.1.4.3 3.1.4.3] Structure known Active Sites: ZN1, ZN2, ZN3 and ZN4. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1QM6 OCA].  

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