Membrane binding of the colicin E1 channel: activity requires an electrostatic interaction of intermediate magnitude.
AUTOR(ES)
Zakharov, S D
RESUMO
In vitro channel activity of the C-terminal colicin E1 channel polypeptide under conditions of variable electrostatic interaction with synthetic lipid membranes showed distinct maxima with respect to pH and membrane surface potential. The membrane binding energy was determined from fluorescence quenching of the intrinsic tryptophans of the channel polypeptide by liposomes containing N-trinitrophenyl-phosphatidylethanolamine. Maximum in vitro colicin channel activity correlated with an intermediate magnitude of the electrostatic interaction. For conditions associated with maximum activity (40% anionic lipid, I = 0.12 M, pH 4.0), the free energy of binding was delta G approximately -9 kcal/mol, with nonelectrostatic and electrostatic components, delta Gnel approximately -5 kcal/mol and delta Gel approximately -4 kcal/mol, and an effective binding charge of +7 at pH 4.0. Binding of the channel polypeptide to negative membranes at pH 8 is minimal, whereas initial binding at pH 4 followed by a shift to pH 8 causes only 3-10% reversal of binding, implying that it is kinetically trapped, probably by a hydrophobic interaction. It was inferred that membrane binding and insertion involves an initial electrostatic interaction responsible for concentration and binding to the membrane surface. This is followed by insertion into the bilayer driven by hydrophobic forces, which are countered in the case of excessive electrostatic binding.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1225257Documentos Relacionados
- Membrane-bound state of the colicin E1 channel domain as an extended two-dimensional helical array
- Dynamic properties of membrane proteins: reversible insertion into membrane vesicles of a colicin E1 channel-forming peptide.
- Membrane topography of ColE1 gene products: the hydrophobic anchor of the colicin E1 channel is a helical hairpin.
- Interaction of 125I-Labeled Colicin E1 with Escherichia coli
- Determination of the molecularity of the colicin E1 channel by stopped-flow ion flux kinetics.