Disintegration of Microtubules into Protofilaments and Ring-Shaped Structure Formation Induced by Kif2C Neck Region Peptide

Members of the kinesin-13 subfamily, including KIF2C, are known to depolymerize microtubules from both ends. The positive charge-rich region extending from N-side of the catalytic head, called the “neck” region, is considered to be important in the depolymerization activity. To obtain clues to functions of the KIF2C neck region, we synthesized several peptide segments derived from the neck region and examined their properties. When a three time molar equivalent of a 37 amino-acid residue peptide, KF01 (around E200), or another peptide consisting of the N-terminal half of KF01, namely, KF11, was mixed with microtubules, the turbidity of the mixture increased steeply. We confirmed the binding of KF01 to microtubules by coprecipitation experiments. Circular dichroism spectroscopy showed that the neck region peptides formed a characteristic secondary structure when they were mixed with microtubules. Electron microscopy revealed that KF01 had the ability to bundle microtubules. Furthermore, at a higher peptide concentration, we detected the presence of thin filaments, considered to be free protofilaments disintegrated from microtubules, and ring-shaped structures surrounding the microtubules, considered to consist of protofilaments. Although a similar ring formation has previously been reported to be induced by the head domain of KIF2C or KLP10A, a member of the kinesin-13 subfamily, the present study has shown for the first time that the peptide derived from the neck region can induce the formation of the rings even without a catalytic head. The KF01-induced disintegration of microtubules into protofilaments would reflect the importance of the neck region to microtubule depolymerization mechanism by the intact KIF2C protein.