Importance of the Converter Region for the Motility of Myosin as Revealed by the Studies on Chimeric Chara Myosins

A long α-helix in myosin head constitutes a lever arm together with light chains. It is known from X-ray crystallographic studies that the first three turns of this lever arm α-helix are inserted into the converter region of myosin. We previously showed that chimeric Chara myosin in which the motor domain of Chara myosin was connected to the lever arm α-helix of Dictyostelium myosin had motility far less than that expected for the motor domain of Chara myosin. Here, we replaced the inserted three turns of α-helix of Dictyostelium myosin with that of the Chara myosin and found that the replacement enhanced the motility 2.6-fold without changing the ATPase activity so much. The result clearly showed the importance of interaction between the converter region and the lever arm α-helix for the efficient motility of myosin.