Dedicated to Professor Lutz F. Tietze Helical secondary structures are a fundamental part of protein architecture and are widely involved in recognition and binding processes between proteins or between proteins and nucleic acids. [1] Furthermore, the organization of peptide helices in bundles is common for the membrane-spanning domains of transmembrane proteins and for many soluble proteins. [2] Peptide helices can be used as templates for specific preorganization of peptides in ligation. [3] The design of amphiphilic helices is important for model studies related to these complex biomolecular interactions. [3, 4] Among apeptides usually about 15-20 amino acids are needed for significant degree of helical secondary structure in aqueous solution. In contrast, six b-amino acids are enough for a substantial population of a b-peptide 14-helix conformation. [5] This b-peptide helix has approximately three residues per turn and a pitch of about 5 . The 14-helix is preferentially formed by b-amino acids with side chains in the b position of the respective amino acids ("b 3 -residues"), and the 14-helix is stabilized dramatically by the inclusion of cyclohexanederived b-amino acid residues. The 14-helix contains hydrogen bonds between NÀH and C=O groups in the b-peptide backbone resulting in the formation 14-membered rings. [6] The regularity of the 14-helix makes it especially suitable as a scaffold for the defined orientation of functional groups appended as b-amino acid side chains.
In a step towards forming an artificial helical-bundle tertiary structure it was recently shown that a 10-residue amphiphilic b-peptide forms small soluble aggregates in water, driven by hydrophobic interactions between the helices. [7] As an extension of this concept, it should be possible to organize small b-peptide helices by nucleobase
[*] Prof.