Construction of a Quadrangular Tetramer and a Cage-Like Hexamer from Three-Helix Bundle-Linked Fusion Proteins.

Self-assembled protein nanostructures have gained interest, owing to their potential applications in biomaterials; however, successful design and construction of protein nanostructures are limited. Herein, we constructed fusion protein 1 by linking the C-terminus of a dimerization domain and the N-terminus of another dimerization domain with a three-helix bundle protein, where it self-assembled mainly into tetramers. By replacing the C-terminal dimerization domain of 1 with a trimerization domain (fusion protein 2), hexamers were mainly obtained. According to ab initio structural models reconstructed from the small-angle X-ray scattering data, the tetramer of 1 and hexamer of 2 adopted quadrangle and cage-like structures, respectively, although they were combinations of different conformations. High-speed atomic force microscopy observations indicated that the tetramer and hexamer exhibit conformational dynamics. These results show that the present method utilizing three-helix bundle-linked fusion proteins is useful in the construction of protein nanostructures.