Free Energy Landscape of Lipid Interactions with Regulatory Binding Sites on the Transmembrane Domain of the EGF Receptor.

George Hedger,Heidi Koldsø,David Shorthouse,Mark S P Sansom

doi:10.1021/acs.jpcb.6b01387

George Hedger, Heidi Koldsø + Show 2 more

Open Access

https://doi.org/10.1021/acs.jpcb.6b01387

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Abstract

Lipid molecules can bind to specific sites on integral membrane proteins, modulating their structure and function. We have undertaken coarse-grained simulations to calculate free energy profiles for glycolipids and phospholipids interacting with modulatory sites on the transmembrane helix dimer of the EGF receptor within a lipid bilayer environment. We identify lipid interaction sites at each end of the transmembrane domain and compute interaction free energy profiles for lipids with these sites. Interaction free energies ranged from ca. −40 to −4 kJ/mol for different lipid species. Those lipids (glycolipid GM3 and phosphoinositide PIP2) known to modulate EGFR function exhibit the strongest binding to interaction sites on the EGFR, and we are able to reproduce the preference for interaction with GM3 over other glycolipids suggested by experiment. Mutation of amino acid residues essential for EGFR function reduce the binding free energy of these key lipid species. The residues interacting with the lipids in the simulations are in agreement with those suggested by experimental (mutational) studies. This approach provides a generalizable tool for characterizing the interactions of lipids that bind to specific sites on integral membrane proteins.

Highlights

The complexity and diversity of cell membrane compositions suggest that lipids may bind to membrane proteins at specific sites and modulate their function
In a number of cases, structural data have been coupled to functional analysis, and it is clear that several classes of membrane protein, including, e.g., K+ channels, receptor tyrosine kinases (RTKs), and G-protein coupled receptors, are regulated via selective interactions with specific lipids.[2−4] there is a need to better characterize these interactions to fully understand the influence of the surrounding membrane environment on membrane protein structure and function.[5]
These lipid interaction hotspots identified by our simulations agree well with in vivo mutagenesis studies and in vitro functional assays that have shown that these residues are essential for the sensitivity of EGFR to GM3 and PIP2.4,8 Visual inspection of the trajectory revealed that once associated each PIP2 lipid molecule remained bound over the 2 μs duration of the simulation

Summary

Introduction

The complexity and diversity of cell membrane compositions suggest that lipids may bind to membrane proteins at specific sites and modulate their function. The epidermal growth factor receptor (EGFR/ErbB1) is perhaps the best characterized member of the human RTK family. It resides in the plasma membrane, where it serves an essential role in transmitting information on the cellular environment to intracellular signaling networks, which subsequently elicit a response.[6] Mutations of the receptor have been implicated in a variety of cancers and the EGFR is a target for therapeutic intervention.[7] Of particular interest, EGFR is known to be modulated by its surrounding lipid environment. The emerging picture is that this modulation may occur via specific lipid interactions,[4,8] in addition to the more general influences of lipids such as cholesterol on the biophysical properties of the membrane.[9]

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