Asymmetry in protein structures

The asymmetry of L-amino acids determines the asymmetrical features of alpha-helices and beta-sheets. These in turn determine two principal aspects of the three-dimensional structure of proteins: the preferred ways in which alpha-helices and beta-sheets pack together, and certain topological features of the paths followed by polypeptide chains through structures. Though the asymmetrical nature of amino acids plays the central role in determining the asymmetrical aspects of protein structures, it has little or no influence on the next level of biological structures--assemblies of protein molecules.