Linear growth of self-assembled alternating oligopeptide nanotubes with self-locking building blocks

An oligopeptide was designed using molecular modelling to self-assemble into nanotubes without forming bundles. An alternating peptide of two glutamic acids (E) and one phenylalanine (F) forms a linear, rigid backbone with phenyl groups sticking out in a propeller-like conformation. At neutral pH, a hydrogen bond forms between two adjacent glutamic acid moieties, forming a closed ring, allowing 32 (EEF) oligopeptides to self-associate by pi-stacking into short nanotube segments with an inner diameter of 4.2 nm and an outer diameter of 8.9 nm. The computational models predict that the nanotubes grow longitudinally by joining the LEGO block-like segments together, in principle to any length. The protruding glutamic acid ring prevents nanotube bundling, guaranteeing long nanotubes of the same diameter as the individual segments. Changing the pH introduces flexibility in the backbone and inhibits self-assembly. The computationally predicted structures are validated experimentally, and rod-like particles with diameter of 10 +/- 0.1 nm and length of 430 +/- 30 nm were observed in Transmission Electron Microscopy. The hollow nanotube interior from oligopeptides, predicted by the models, is a promising avenue to template structures or modify chemical reactivity.