GroEL(SP/MC), prepared by genetic and chemical modifications of group I chaperonin protein GroEL, site-specifically possesses similar to 28 photochromic (spiropyran [SP] and merocyanine [MC]) units in the entrance parts of its cavity. Addition of divalent metal ions such as Mg2+ to a tris-HCl buffer solution of GroEL(SP/MC) results in one-dimensional (1D) assembly of GroEL(SP/MC), affording cylindrical hollow fibers with a very large aspect ratio; the longest fiber was similar to 2.5 mu m tong, corresponding to a 170-mer of GroEL(SP/MC) (MW approximate to 1.4 x 10(8)). When such tong fibers are mixed with EDTA, they are cut into short-chain oligomers and eventually into monomeric GroEL(SP/MC). Similar to GroEL, GroEL(SP/MC) possesses a large binding affinity toward denatured proteins. When GroEL(SP/MC) undergoes 1D assembly after incubation with a denatured protein, guest-containing cylindrical fibers result.