Bioengineered flagella protein nanotubes with cysteine loops: self-assembly and manipulation in an optical trap.

An E. coli flagellin protein, termed FliTrx, was investigated for use as a novel form of self-assembling protein nanotube. This protein was genetically engineered to display constrained peptide loops with a series of different thiol, cationic, anionic, and imidazole functional groups. "Cys-loop" thiol variants consisting of 6 and 12 cysteine residues were isolated in the form of disulfide-linked nanotube bundles, a novel nanomaterial. Bundles were characterized by fluorescence microscopy, transmission electron microscopy, and optical trapping.