ACCELERATED COMMUNICATIONS Effects of aligned a-helix peptide dipoles on experimental electrostatic potentials

Aligned protein a-helix dipoles have been implicated in protein function and structure. The recent breakthroughs in high-resolution electron microscopy (EM) of macromolecules makes it possible to explore fundamental aspects of structural biology at the detailed molecular level. The electrostatic potential (ESP) generated by aligned protein a-helix dipole should be observable in high-resolution EM maps despite the fact that the effect may be partially screened by induced electric fields. Here, we show that aligned backbone dipoles in protein a-helices account for long-range features in the protein ESP functions. Our results are consistent with experimental EM maps and density functional theory calculations, including direct Fourier summation for proper calculation of the ESP due to the nonlocal nature of the ESP function from aligned dipoles and other partial atomic charges.