Open AccessProtein-lipid interactions in bilayer membranes: A lattice model
Author(s) -
David A. Pink,
D. Chapman
Publication year - 1979
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.76.4.1542
Subject(s) - chemistry , enthalpy , polar , chemical physics , lipid bilayer , steric effects , bilayer , thermodynamics , van der waals force , eutectic system , lipid bilayer phase behavior , phase transition , crystallography , membrane , stereochemistry , molecule , organic chemistry , physics , biochemistry , microstructure , astronomy
A lattice model has been developed to study the effects of intrinsic membrane proteins upon the thermodynamic properties of a lipid bilayer membrane. We assume that only nearest-neighbor van der Waals and steric interactions are important and that the polar group interactions can be represented by effective pressure—area terms. Phase diagrams, the temperatureT 0 , which locates the gel—fluid melting, the transition enthalpy, and correlations were calculated by mean field and cluster approximations. Average lipid chain areas and chain areas when the lipid is in a given protein environment were obtained. Proteins that have a “smooth” homogeneous surface (“cholesterol-like”) and those that have inhomogeneous surfaces or that bind lipids specifically were considered. We find thatT 0 can vary depending upon the interactions and that another peak can appear upon the shoulder of the main peak which reflects the melting of a eutectic mixture. The transition enthalpy decreases generally, as was found before, but when a second peak appears departures from this behavior reflect aspects of the eutectic mixture. We find that proteins have significant nonzero probabilities for being adjacent to one another so that no unbroken “annulus” of lipid necessarily exists around a protein. IfT 0 does not increase much, or decreases, with increasingc , then lipids adjacent to a protein cannot all be all-trans on the time scale (10-7 sec) of our system. Around a protein the lipid correlation depth is about one lipid layer, and this increases withc . Possible consequences of ignoring changes in polar group interactions due to clustering of proteins are discussed.