Nanotubes, Plates, and Needles: Pathway-Dependent Self-Assembly of Computationally Designed Peptides.

Computationally designed peptides form desired antiparallel, tetrameric coiled-coil bundles that hierarchically assemble into a variety of well-controlled nanostructures depending on aqueous solution conditions. The bundles selectively self-assemble into different structures: nanotubes, platelets, or needle-like structures at solution pH values of 4.5, 7, and 10, respectively. The self-assembly produces hollow tubes or elongated needle-like structures at pH conditions associated with charged bundles (pH 4.5 or 10); at neutral pH, near the pI of the bundle, a plate-like self-assembled structure forms. Transmission electron microscopy and small-angle X-ray scattering show the nanotubes to be uniform with a tube diameter of ∼13 nm and lengths of up to several μm, yielding aspect ratios >1000. Combining the measured nanostructure geometry with the apparent charged states of the constituent amino acids, a tilted-bundle packing model is proposed for the formation of the homogeneous nanotubes. This work demonstrates the successful use of assembly pathway control for the construction of nanostructures with diverse, well-structured morphologies associated with the folding and self-association of a single type of molecule.