Dielectric Properties of Proteins

We have developed a theory for the anisotropic and inhomogeneous dielectric properties of proteins. Using a generalization of dielectric theories of polar solids and liquids, we have calculated the mesoscopic, spatially-varying dielectric constant at points in and around a protein by combining the Kirkwood–Fro ̈hlich theory with short all-atom molecular dynamics simulations of equilibrium protein fluctuations. The resulting dielectric permittivity tensor is found to exhibit significant heterogeneity and anisotropy in the protein interior.

The spatially-varying dielectric function for adenylate kinase (1AKY). Shown is the effective scalar dielectric constant on a horizontal plane through the geometric center of the protein.

Around the surface of the protein it may exceed the dielectric constant of bulk water, especially near the mobile side chains of polar residues, such as K, N, Q, and E.

Dielectric contours around the 1AKY structure, showing surfaces of epsilon = 5, 25, 70 and 80. Regions inside the blue globules have dielectric constants larger than that of water.

The anisotropic character of the protein dielectric selectively modulates the attractions and repulsions between charged groups in close proximity.

Anisotropy in the dielectric tensor epsilon. The orientation of each ellipsoid is given by the eigenbasis of the dielectric tensor at that point; the lengths of the semimajor axes are directly proportional to the eigenvalues of the tensor. Only ellipsoids with a difference between eigenvalues of >25% are shown.

References

Guest W, Cashman NR, Plotkin SS, “A Theory for the Anisotropic and Inhomogeneous Dielectric Properties of Proteins” Phys. Chem. Chem. Phys., 13 (13), 6286 – 6295 (2011)

Guest W, Cashman NR, Plotkin SS, “Electrostatics in the Stability and Misfolding of the Prion Protein: Salt Bridges, Self-Energy, and Solvation” Biochem. Cell Biol 88, 371–381 (2010)