Photoreconfigurable Supramolecular Nanotube

A photoreconfigurable bionanotube was developed by Mg²⁺-induced supramolecular polymerization using GroEL_SP, a mutant barrel-shaped chaperonin protein bearing multiple photochromic spiropyran (SP) units at its apical domains. Upon exposure to UV light, the nonionic SP units isomerize into ionic merocyanine (MC) to afford GroEL_MC, which is capable of polymerizing with MgCl₂. The resultant nanotube (NT) is stable as a result of multiple MC···Mg²⁺···MC bridges but readily breaks up into short NTs, including monomeric GroEL_SP, by the reverse (MC → SP) isomerization mediated by visible light. When this scission mixture is exposed to UV light, long NTs are reconfigured. A Förster resonance energy transfer (FRET) study revealed that NTs in the dark maintain their sequential integrity. However, when exposed to visible and UV light successively, the NTs lose their sequential memory as a result of intertubular reshuffling of the constituent GroEL_MC units.