BIOMECHANICS AT MICRO- AND NANOSCALE LEVELS - Volume IV © World Scientific Publishing Co. Pte. Ltd. http://www.worldscibooks.com/engineering/6593.html 3 STRUCTURAL ANALYSIS OF THE MOTOR PROTEIN PRESTIN H. WADA, K. IIDA, M. MURAKOSHI AND S. KUMANO Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai 980-8579, Japan E-mail: wada@cc.mech.tohoku.ac.jp K. TSUMOTO Department of Medical Genome Sciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8651, Japan K. IKEDA Department of Otorhinolaryngology, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan I. KUMAGAI Department of Biomolecular Engineering, Tohoku University, 6-6-07 Aoba-yama, Sendai 980-8579, Japan T. KOBAYASHI Department of Otorhinolaryngology, Head and Neck Surgery, Tohoku University, Graduate School of Medicine, 1-1 Seiryo-machi, Sendai 980-8675, Japan The high sensitivity of human hearing is believed to be achieved by cochlear amplification. The basis of this amplification is thought to be the motility of mammalian outer hair cells (OHCs), i.e., OHCs elongate and contract in response to acoustical stimulation. This motility is made possible by the motor protein prestin, which is embedded in the lateral membrane of OHCs. Amino acid sequence analyses showed that prestin is a member of solute carrier (SLC) 26 family. However, information on the structure and function of prestin is limited. In the present study, therefore, attempts were made to generate stable prestin-expressing cell lines using Chinese hamster ovary (CHO) cells and to visualize prestin molecules expressed in their plasma membrane by atomic force microscopy. Results indicate that cell lines stably expressing prestin, the activity of which was confirmed, could be established and that the particle-like structures with a diameter of 8–12 nm observed in their plasma membranes are possibly prestin. In addition, to clarify the mechanism by which prestin functions, mutational analysis of prestin was performed. Results show that the GTSRH sequence highly conserved in the SLC26 family is important for the correct folding of prestin. 1 Introduction The mammalian ear is characterized by its high sensitivity and sharp frequency selectivity, which are believed to be based on the amplification of basilar membrane vibration in the cochlea. This cochlear amplification is actuated by the motility of