Helix-helix interactions in lipid bilayers

Nir Ben-Tal, Barry Honig*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Using a continuum model, we calculated the electrostatic interaction free energy between two α-helices in three environments; the aqueous phase, a low dielectric alkane phase, and a simple representation of a lipid bilayer. As was found in previous work, helix-helix interactions in the aqueous phase are quite weak, because of solvent screening, and slightly repulsive, because of desolvation effects that accompany helix assembly. In contrast, the interactions can be quite strong in a hypothetical alkane phase because desolvation effects are essentially nonexistent and because helix- helix interactions are not well screened. In this type of environment, the antiparallel helix orientation is strongly favored over the parallel orientation. In previous work we found that the free energy penalty associated with burying helix termini in a bilayer is quite high, which is why the termini tend to protrude into the solvent. Under these conditions the electrostatic interaction is strongly screened by solvent; indeed, it is sufficient for the termini to protrude a few angstroms from the two surfaces of the bilayer for their interaction to diminish almost completely. The effect is consistent with the classical model of the helix dipole in which the dipole moment is represented by point charges located at either terminus. Our results suggest, in agreement with previous models, that there is no significant nonspecific driving force for helix aggregation and, hence, that membrane protein folding must be driven by specific interactions such as close packing and salt-bridge and hydrogen bond formation.

Original languageEnglish
Pages (from-to)3046-3050
Number of pages5
JournalBiophysical Journal
Volume71
Issue number6
DOIs
StatePublished - Dec 1996
Externally publishedYes

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