Characteristic Properties of Novel Photochromic Inhibitor of Kinesin Eg5 Composed of Spiropyran Derivative

Abstract

Kinesin Eg5 which is a kind of motor protein has an important role on the cell division. Eg5 tetramer crosslinks with anti-parallel microtubule and induce formation of bipolar spindle in M phase. It is known that kinesin Eg5 overexpress in some of cancer cells. Kinesin Eg5 has been considered as a target of anti-cancer therapy. Several small molecules were recognized as potent inhibitors of Eg5. Interestingly the inhibitors bind to the common pocket in Eg5 motor domain. STLC is one of the well-known potent inhibitor of Eg5. The crystallographic structure of Eg5-STLC complex revealed that STLC binds to the pocket composed of α2, α3 helix and loop L5. The inhibitory mechanism of STLC has been well studied. Photochromic molecules such as azobenzene and spiropyran derivatives, which change their structures and properties reversibly by light irradiation, are expected to be applicable to photo-switches of bionanomachines. Previously we have demonstrated that STLC analogues composed of azobenzenen (ACTAB) or spiropyran (SP-APA) inhibit Eg5 ATPase activity and motor activity photo-reversibly upon UV and visible light irradiations. Moreover, HeLa cell division was photo-regulated with ACTAB. In this study, we have tried to study the optimum conditions to regulate the function of Eg5 with the photochromic inhibitors we have synthesized. In the results, pH and ionic strength dependent effect of the inhibitors on the ATPase activity and Eg5 driven microtubule gliding. At pH6.8, SP-APA showed significant efficiency to control ATPase and motor activities as an inhibitor that has a photo-switching system.