Parity-violation energy of biomolecules-IV: protein secondary structure.

The parity-violation energy difference between enantiomeric forms of the same amino acid sequence, from the amyloid β-peptide involved in Alzheimer's disease, in both α-helix and β-sheet configurations, is investigated with ab-initio techniques. To this end, we develop an extension of the N2 computational scheme that selectively includes neighboring amino acids to preserve the relevant H-bonds. In agreement with previous speculations, it is found that the helical α structure is associated with larger parity-violation energy differences than the corresponding β form. Implications for the evolution of biological homochirality are discussed as well as the relative importance of various effects in determining the parity-violation energy.