15 research outputs found
Molecular theory of hydrophobic mismatch between lipids and peptides
Effects of the mismatch between the hydrophobic length, d, of transmembrane
alpha helices of integral proteins and the hydrophobic thickness, D_h, of the
membranes they span are studied theoretically utilizing a microscopic model of
lipids. In particular, we examine the dependence of the period of a lamellar
phase on the hydrophobic length and volume fraction of a rigid, integral,
peptide. We find that the period decreases when a short peptide, such that
d<D_h, is inserted. More surprising, we find that the period increases when a
long peptide, such that d>D_h, is inserted. The effect is due to the
replacement of extensible lipid tails by rigid peptide. As the peptide length
is increased, the lamellar period continues to increase, but at a slower rate,
and can eventually decrease. The amount of peptide which fails to incorporate
and span the membrane increases with the magnitude of the hydrophobic mismatch
|d-D_h|. We explicate these behaviors which are all in accord with experiment.
Predictions are made for the dependence of the tilt of a single trans-membrane
alpha helix on hydrophobic mismatch and helix density.Comment: 14 pages, 5 figure
Using mean field theory to determine the structure of uniform fluids
The structure of a uniform simple liquid is related to that of a reference
fluid with purely repulsive intermolecular forces in a self-consistently
determined external reference field (ERF) phi_ R. The ERF can be separated into
a harshly repulsive part phi_ R0 generated by the repulsive core of a reference
particle fixed at the origin and a more slowly varying part phi_ R1 arising
from a mean field treatment of the attractive forces. We use a generalized
linear response method to calculate the reference fluid structure, first
determining the response to the smoother part phi_ R1 of the ERF alone,
followed by the response to the harshly repulsive part. Both steps can be
carried out very accurately, as confirmed by MD simulations, and good agreement
with the structure of the full LJ fluid is found.Comment: 11 pages, 7 figure
Density fluctuations and the structure of a nonuniform hard sphere fluid
We derive an exact equation for density changes induced by a general external
field that corrects the hydrostatic approximation where the local value of the
field is adsorbed into a modified chemical potential. Using linear response
theory to relate density changes self-consistently in different regions of
space, we arrive at an integral equation for a hard sphere fluid that is exact
in the limit of a slowly varying field or at low density and reduces to the
accurate Percus-Yevick equation for a hard core field. This and related
equations give accurate results for a wide variety of fields