1QMD

calcium bound closed form alpha-toxin from Clostridium perfringens

Summary for 1QMD

• Entry DOI: 10.2210/pdb1qmd/pdb
• Related: 1AH7 1CA1 1QM6
• Descriptor: PHOSPHOLIPASE C, ZINC ION, CALCIUM ION, ... (4 entities in total)
• Functional Keywords: hydrolase, zinc phospholipase c, gangrene determinant, c2 domain, ca and membrane binding.
• Biological source: CLOSTRIDIUM PERFRINGENS
• Total number of polymer chains: 2
• Total formula weight: 85657.74

Authors

Naylor, C.E.,Miller, J.,Titball, R.W.,Basak, A.K. (deposition date: 1999-09-27, release date: 2000-02-06, Last modification date: 2023-12-13)

Primary citation

Naylor, C.E.,Jepson, M.,Crane, D.T.,Titball, R.W.,Miller, J.,Basak, A.K.,Bolgiano, B.
Characterisation of the Calcium-Binding C-Terminal Domain of Clostridium Perfringens Alpha-Toxin
J.Mol.Biol., 294:757-, 1999

PubMed Abstract: 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.

PubMed: 10610794
DOI: 10.1006/JMBI.1999.3279

Experimental method

X-RAY DIFFRACTION (2.2 Å)