2i88
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(New page: 200px<br /><applet load="2i88" size="450" color="white" frame="true" align="right" spinBox="true" caption="2i88, resolution 2.5Å" /> '''Crystal structure of ...)
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Revision as of 10:04, 21 November 2007
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Crystal structure of the Channel-forming Domain of Colicin E1
Overview
BACKGROUND: Channel-forming colicins, including colicin E1, are a, sub-family of bacteriocins. The toxic action of colicin E1 is derived from, its ability to form a voltage-gated channel, which causes depolarization, of the cytoplasmic membrane of sensitive Escherichia coli cells. In this, process, the toxin-like colicin E1 molecule must undergo a substantial, structural transition from a soluble state, in which it binds the target, cell, to a membrane-bound state. Details of the structural changes that, accompany this conversion may be directly applicable to other, channel-forming toxins, as well as to the mechanism by which proteins, insert into or cross membranes. RESULTS: The structure of the 190-residue, channel-forming domain of colicin E1 in its soluble form has been solved, at 2.5 A resolution. This structure contains 10alpha helices arranged in, three layers (A-C) with a central hydrophobic helical hairpin in layer B, which is proposed to anchor the membrane-bound form in the bilayer. The, extended N-terminal helix I provides a connection to the rest of the, colicin E1 molecule, and the loop I-II may act as a hinge for, re-orientation of the domain for membrane binding. A set of conserved, positively charged residues on layer C may provide the docking surface on, the molecule for membrane attachment. A large internal cavity between, layers B and C may allow these layers to disengage, suggesting a mechanism, for unfolding the molecule on the membrane that involves the perturbation, of the interhelical hydrophobic interactions in layer C. CONCLUSION: On, the basis of the structure of the colicin E1 channel-forming domain, its, comparison with the structure of the colicin A domain and the known, requirement for initial electrostatic and subsequent hydrophobic, interactions, molecular details of the docking, unfolding and insertion of, the channel-forming domain into the membrane are proposed. The model for, docking and initial interaction with the membrane positions the, hydrophobic hairpin 'anchor' approximately parallel to the membrane, surface. Hydrophobic interactions in the docking layer may then be, displaced by interactions with the membrane, spreading the helices on the, surface and exposing the hydrophobic hairpin for insertion into the, membrane.
About this Structure
2I88 is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.
Reference
A mechanism for toxin insertion into membranes is suggested by the crystal structure of the channel-forming domain of colicin E1., Elkins P, Bunker A, Cramer WA, Stauffacher CV, Structure. 1997 Mar 15;5(3):443-58. PMID:9083117
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