Quadruple peptide helices

Quadruple peptide helices have also been made by self-assembly in water. The designed amino acid 16-meric sequence GELEELLKKLKELLKG forms an amphiphilic helix and should form a four-helix bundle or quadruple helix by assembly of the hydrophobic leucine segments. It was indeed found experimentally that the ellipticity in the CD spectrum increased with the fourth power of the peptide concentration. The helices were only formed if there was a chance of tetramerization (Eisenberg et al., 1986). 

Muraoka T, Cui H, Stupp SI (2008) Quadruple helix formation of a photoresponsive peptide amphiplule and its light-triggered dissociation into single fibers. J Am Chem Soc 130 2946-2947... 

Figure 9.6.11 A quadruple helix on a macrocyclic peptide containing few lysine (K) units.

Ac-E-L-E-K-L-L-X-E-L-E-K-L-L-K-E-L-E-K-amide, an amphipathic a-helical peptide, where X is substituted by leucine (LL7), valine (LV7), threonine (LT7), or serine (LS7), i.e., substitutions are made in the hydrophilic face of the helix cyclo-V-X-L-Y-P-V-X-L-Y-P), where X is substituted by diaminopropionic acid (Dap), diaminobutyric acid (Dab), ornithine (Orn), lysine (Lys), arginine (Arg), or histidine (His) Cyclo-(V-K-L-K-V-Y-P-L-K-V-K-L-Y-P), where 14 analogues were produced by single enantiomeric substitutions at each residue around the ring an extra two analogues were produced by double or quadruple enantiomeric substitutions of the lysine (K) residues... 

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