  Amide resonance is found to be sensitive to electrostatic field with
component parallel or antiparallel to the amide C-N bond, an effect we refer to
here as EVPR-CN. EVPR-CN is linear and without threshold in the biologically
plausible electrostatic field range -0.005 to 0.005 au. Variation of amide
resonance varies Resonance-Assisted Hydrogen Bonding such as occurs in the
hydrogen bonded chains of backbone amides of protein secondary structures such
as beta sheets and alpha helices, varying the stability of these structures.
The electrostatic properties including permittivity of amino acid residue
sidegroups influence the electrostatic field component parallel or antiparallel
to the C-N bond of each amide, giving a novel relationship between residue
sequence and protein structure. Additionally, a backbone-based theory of
protein folding which includes this effect is presented in Section 8.4.
  The significance of EVPR-CN relative to other factors in protein folding
depends on field C-N component at each backbone amide at a given time.
Calculation indicates that backbone amides do not occupy an intrinsically
electrostatically-protected niche. We propose that EVPR-CN warrants
investigation in any study of stable protein structure or protein folding
pathway. EVPR-CN is somewhat associated with hydrophobia, since hydrophobia
creates low permittivity environments. EVPR-CN is more directionally and hence
structurally specific than hydrophobia.
  Hypotheses concerning the stability of beta sheets and amyloid fibrils and of
protein complexation and molecular chaperone function are offered. An analogous
effect in nitrogenous base pairing is proposed.
  EVPR-CN is energetically significant in biologically plausible electrostatic
fields even without considering a hydrogen bonding context, and a hypothesis
concerning the stability of polyproline helices types I and II is offered.
