Membrane transporter dimerization driven by differential lipid solvation energetics of dissociated and associated states

Published

April 7, 2021

Author(s)

Rahul Chadda, Nathan Bernhardt, Elizabeth Kelley, Susana Marujo Teixeira, Kacie Griffith, Alejandro Gil-Ley, Tugba Ozturk, Lauren Hughes, Ana Forsythe, Venkatramanan Krishnamani, Jose Faraldo-Gomez, Janice Robertson

Abstract

Over two-thirds of integral membrane proteins of known structure assemble into oligomers. Yet, the forces that drive the association of these proteins remain to be delineated, as the lipid bilayer is a solvent environment that is both structurally and chemically complex. In this study, we reveal how the lipid solvent defines the dimerization equilibrium of the CLC-ec1 Cl-/H+ antiporter. Integrating experimental and computational approaches, we show that monomers associate to avoid a thinned-membrane defect formed by hydrophobic mismatch at their exposed dimerization interfaces. In this defect, lipids are strongly tilted and less densely packed than in the bulk, with a larger degree of entanglement between opposing leaflets and greater water penetration into the bilayer interior. Dimerization restores the membrane to a near-native state and therefore, appears to be driven by the larger free-energy cost of lipid solvation of the dissociated protomers. Supporting this theory, we demonstrate that addition of short-chain lipids strongly shifts the dimerization equilibrium toward the monomeric state, and show that the cause of this effect is that these lipids preferentially solvate the defect. Importantly, we show that this shift requires only minimal quantities of short-chain lipids, with no measurable impact on either the macroscopic physical state of the membrane or the protein's biological function. Based on these observations, we posit that free-energy differentials for local lipid solvation define membrane-protein association equilibria. With this, we argue that preferential lipid solvation is a plausible cellular mechanism for lipid regulation of oligomerization processes, as it can occur at low concentrations and does not require global changes in membrane properties.

Citation

eLIFE

Volume

10

Pub Type

Journals

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DOI Link

Keywords

lipid solvation, protein dimerization, CLC dimer, lipid solvation

Citation

Chadda, R. , Bernhardt, N. , Kelley, E. , Marujo Teixeira, S. , Griffith, K. , Gil-Ley, A. , Ozturk, T. , Hughes, L. , Forsythe, A. , Krishnamani, V. , Faraldo-Gomez, J. and Robertson, J. (2021), Membrane transporter dimerization driven by differential lipid solvation energetics of dissociated and associated states, eLIFE, [online], https://doi.org/10.7554/eLife.63288 (Accessed April 28, 2024)