Generation of stable microtubule superstructures by binding of peptide-fused tetrameric proteins to inside and outside
Microtubules (MTs) play important roles in biological functions by forming superstructures, such as doublets, triplets, and branched structures, in vivo. Formation of these superstructures by exogenous molecules in vitro will be useful not only for understanding the functions of MTs but also as components of MT-based nanomaterials. Here, we developed a tetrameric fluorescent protein Azami-Green (AG) fused with a His-tag and Tau-derived peptide (TP), TP-AG, which can bind to the inside or outside of MTs depending on the polymerization conditions. The binding of TP-AG to the inside of MTs induced the formation, stabilized, and increased the rigidity of the MTs. The binding of TP-AG to the outside of MTs induced various types of MT superstructures, including doublets, multiplets, and branched structures, by recruiting tubulins to MTs. The formation of motile MT aster structures by TP-AG was also observed. The generation of MT superstructures by these exogenous proteins provides guidelines for the design of MT-based nanomaterials.