Pre-transition effects mediate forces of assembly between transmembrane proteins
Shachi Katira,
Kranthi K Mandadapu,
Suriyanarayanan Vaikuntanathan,
Berend Smit,
David Chandler
Affiliations
Shachi Katira
Department of Chemistry, University of California, Berkeley, Berkeley, United States
Kranthi K Mandadapu
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, United States; Department of Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, United States
Suriyanarayanan Vaikuntanathan
Department of Chemistry, University of Chicago, Chicago, United States
Berend Smit
Department of Chemistry, University of California, Berkeley, Berkeley, United States; Department of Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, United States; Laboratory of Molecular Simulation, Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, Sion, Switzerland
David Chandler
Department of Chemistry, University of California, Berkeley, Berkeley, United States
We present a mechanism for a generic, powerful force of assembly and mobility for transmembrane proteins in lipid bilayers. This force is a pre-transition (or pre-melting) effect for the first-order transition between ordered and disordered phases in the membrane. Using large-scale molecular simulation, we show that a protein with hydrophobic thickness equal to that of the disordered phase embedded in an ordered bilayer stabilizes a microscopic order–disorder interface. The stiffness of that interface is finite. When two such proteins approach each other, they assemble because assembly reduces the net interfacial energy. Analogous to the hydrophobic effect, we refer to this phenomenon as the 'orderphobic effect'. The effect is mediated by proximity to the order–disorder phase transition and the size and hydrophobic mismatch of the protein. The strength and range of forces arising from this effect are significantly larger than those that could arise from membrane elasticity for the membranes considered.
