Do parallel β‐strands have dipole moments? An ab initio molecular‐orbital‐direct reaction field study

Recently, it was suggested that parallel β‐sheets have a significant dipole moment, in contrast to antiparallel sheets. Ab initio molecular‐orbital (MO) calculations on parallel and antiparallel β‐strands of tetra(Gly) show that they have very similar charge distributions. Interaction energies between two and three strands of tetra(Gly), obtained using the direct reaction field Hamiltonian, show that a particular choice of point charges is probably not crucial for calculating interactions within β‐sheets, but that it might be for calculating interactions between these sheets and other parts of a protein, in particular, α‐helices. The point‐charge representation of our MO‐SCF results will probably reduce the hazard of introducing artefacts in electrostatic calculations of protein conformational energies, provided the short‐range interactions are treated in a more realistic way, i.e., such that intra‐ and interchain induction effects are included