title: The Staphylococcus aureus alpha-toxin channel complex and the effect of Ca2+ ions on its interaction with lipid layers.
abstract: Using the techniques of two-dimensional crystallization on supported lipid bilayers together with computer image processing, two distinct two-dimensional crystal types of staphylococcal alpha-toxin complex are formed depending on the presence or absence of Ca2+ ions. Without Ca2+, these are hexagonally packed (in A, a = b = 89.5 +/- 2.5 A; theta = 119.7 degrees) With Ca2+ present, rectangular crystal packing is seen (in A, a = 114.8 +/- 1.6 A, b = 140.2 +/- 0.7 A; theta = 89.1 degrees). A third, banded crystal type is also seen which is interpreted as a side-to-side packing of regular tubules. We use these tubular crystals for cross-correlation searches with top and side-on views of the complex from single particle reconstructions, and with the repeating units from the two-dimensional crystal types. The results lead us to propose a model in which the different two-dimensional crystal types are formed as a result of alpha-toxin hexamers packing in different orientations. In the hexagonal crystals the hexamers lie end-on with a 6-fold axis in projection. On the addition of Ca2+, the hexamers reorient to lie tilted with respect to the support, thus giving rise to a rectangular projection.
authors.affiliation: European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: R J
authors.initials: RJ
authors.lastname: Ward
authors.forename: K
authors.initials: K
authors.lastname: Leonard
mesh_terms: D001427:Bacterial Toxins / Q000737:chemistry* / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology*; D003460:Crystallization; D005098:Exotoxins / Q000737:chemistry* / Q000378:metabolism; D006460:Hemolysin Proteins / Q000737:chemistry* / Q000378:metabolism; D007091:Image Processing, Computer-Assisted; D008051:Lipid Bilayers / Q000378:metabolism*; D008854:Microscopy, Electron; D011485:Protein Binding / Q000187:drug effects; D013211:Staphylococcus aureus
chemical_list: D001427:Bacterial Toxins; D005098:Exotoxins; D006460:Hemolysin Proteins; D008051:Lipid Bilayers; C021091:staphylococcal alpha-toxin; D002118:Calcium