Browsing by Author "Otaka, Michiro"

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    The ATPase activity of molecular chaperone HSP60 is inhibited by immunosuppressant mizoribine
    (Scientific Research Publishing, 2012-04) Tanabe, Masako; Ishida, Ryuichi; Izuhara, Fumiko; Komatsuda, Atsushi; Wakui, Hideki; Sawada, Kenichi; Otaka, Michiro; Nakamura, Nobuhiro; Itoh, Hideaki
    The molecular chaperone HSP60 is a chaperonin homolog of GroEL. We had previously shown that the immunosuppressant mizoribine is bound directly to HSP60 and inhibited its chaperone activity. However, the inhibitory mechanisms of HSP60 by mizoribine have not yet been fully understood. In the present study, we investigated the influence of mizoribine on a folding cycle of HSP60 and co-chaperone HSP10. Our results showed that mizoribine inhibited the folding cycle of HSP60/HSP10. The ATPase activity of HSP60/HSP10 was decreased in the presence of mizoribine and the dissociation of HSP10 from HSP-60 was also decreased by mizoribine. The same functions of GroEL and/or GroES were slightly affected by mizoribine. Based on our findings, we discuss the inhibitory mechanisms of HSP60 by mizoribine.
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    Cytosolic chaperonin CCT possesses GTPase activity
    (Scientific Research Publishing, 2011-10) Noguchi, Susumu; Toyoshima, Kazuyoshi; Yamamoto, Soh; Miyazaki, Toshio; Otaka, Michiro; Watanabe, Sumio; Imai, Katsunori; Senoo, Haruki; Kobayashi, Ryoji; Jikei, Mitsutoshi; Kawata, Yasushi; Kubota, Hiroshi; Itoh, Hideaki
    Cytosolic chaperonin CCT (also known as TRiC) is a hetero-oligomeric cage-like molecular chaperone that assists in protein folding by ATPase cycle-dependent conformational changes. However, role of the nucleo-tide binding and hydrolysis in CCT-assisted protein folding is still poorly understood. We purified CCT by using ATP-Sepharose and other columns, and found that CCT possesses ability to hydrolyze GTP, with an activity level very similar to the ATPase activity. CCT was more resistant to proteinase K treatment in the presence of GTP or ATP. These results suggest that the GTPase activity of CCT may play a role in chaperone-assisted protein folding.