Box 2 Reflections on self-assembly
The chirality of molecular building blocks plays an important role in self-assembly processes. An example of how chirality at the molecular level influences the supramolecular structures is evident in the self-assembly of an eight-residue peptide, KFE8 (FKFEFKFE)52. The innate right-handed twist of the B-stranded peptide backbone in B-sheet conformation leads to the formation of left-handed double-helical ribbon of regular pitch at the nanometer scale. Chirality in fibrous molecular structures is common. Interestingly, many nanofibers self-assembled from a wide range of peptides and proteins form 10 fibrils with various degrees of left-handed helical twist, regardless of the size of the biomolecules20,84–86. However, the detailed molecular structure of these nanofibers is still difficult to determine because they are not amenable to either single-crystal X-ray diffraction or solution nuclear magnetic resonance at present. New tools will be needed to obtain high resolution of fibrous structures.