Effect of Photoinduced Size Changes on Protein Refolding and Transport Abilities of Soft Nanotubes

Self-assembly of azobenzene-modified amphiphiles (Gly(n)Azo, n=1-3) in water at room temperature in the presence of a protein produced nanotubes with the protein encapsulated in the channels. The Gly(2)Azo nanotubes (7 nm internal diameter [i.d.]) promoted refolding of some encapsulated proteins, whereas the Gly(3)Azo nanotubes (13 nm i.d.) promoted protein aggregation. Although the 20 nm i.d. channels of the Gly(1)Azo nanotubes were too large to influence the encapsulated proteins, narrowing of the i.d. to 1 nm by trans-to-cis photoisomerization of the azobenzene units of the Gly(1)Azo monomers packed in the solid bilayer membranes led to a squeezing out of the proteins into the bulk solution and simultaneously enhanced their refolding ratios. In contrast, photoinduced transformation of the Gly(2)Azo nanotubes to short nanorings (< 40 nm) with a large i.d. (28 nm) provided no further refolding assistance. We thus demonstrate that pertubation by the solid bilayer membrane wall of the nanotubes is important to accelerate refolding of the denatured proteins during their transport in the narrow nanotube channels.