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Specific Interaction between GroEL and Denatured Protein Measured by Compression-Free Force Spectroscopy

Hiroshi Sekiguchi ^*, Hideo Arakawa ^*, Hideki Taguchi , Takeshi Ito , Ryohei Kokawa  and Atsushi Ikai ^*

^* Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Midori-ku, Yokohama, Kanagawa 226-8501, Japan; Chemical Resources Laboratory, Tokyo Institute of Technology, Midori-ku, Yokohama, Kanagawa, 226-8503, Japan; and Research & Development Department, Surface Analysis & Semiconductor Equipment Division, SHIMADZU Corporation, Hadano, Kanagawa 259-1304, Japan

Correspondence: Address reprint requests to Hiroshi Sekiguchi, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8501, Japan. Tel.: +81-45-924-5828; Fax: +81-45-924-5806; E-mail: hsekiguc{at}bio.titech.ac.jp.

We investigated the interaction between GroEL and a denatured protein from a mechanical point of view using an atomic force microscope. Pepsin was bound to an atomic force microscope probe and used at a neutral pH as an example of denatured proteins. To measure a specific and delicate interaction force, we obtained force curves without pressing the probe onto GroEL molecules spread on a mica surface. Approximately 40 pN of tensile force was observed for 10 nm while pepsin was pulled away from the chaperonin after a brief contact. This length of force duration corresponding to the circumference of GroEL's interior cavity was shortened by the addition of ATP. The relation between the observed mechanical parameters and the chaperonin's refolding function is discussed.