1993 Fiscal Year Final Research Report Summary
Regulation of the Functions of GTP-binding Proteins
| Project/Area Number |
04454600
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
代謝生物化学
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| Research Institution | The University of Tokyo (Faculty of Phamaceutical Sciences) (1993)
Tokyo Institute of Technology (1992) |
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Principal Investigator |
KATADA Toshiaki The University of Tokyo, Faculty of Pharmaceutical Sciences, Department of Physiological Chemistry, Professor, 薬学部, 教授 (10088859)
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| Co-Investigator(Kenkyū-buntansha) |
NISHINA Hiroshi Tokyo Institute of Technology, Department of Life Science, Research fellow, 生命理工学部, 助手 (60212122)
TAKAHASHI Katsunobu Tokyo Institute of Technology, Department of Life Science, Research fellow, 生命理工学部, 助手 (40183850)
HOSHINO Shin-ichi The University of Tokyo, Department of Physiological Chemistry, Research fellow, 薬学部, 助手 (40219168)
HAZEKI Osamu The University of Tokyo, Department of Physiological Chemistry, Research fellow, 薬学部, 助手 (80142751)
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| Project Period (FY) |
1992 – 1993
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| Keywords | GTP-binding proteins / Pertussis toxin / Membrane receptors / ADP-ribosylation / Signal transduction / Nuclear transport |
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| Research Abstract |
GTP-binding proteins (G proteins) consisting of alpha, beta and gamma subunits carry signals from membrane receptors to effectors such as enzymes or ion channels. The betagamma subunits initially appeared to be functionally interchangeable with different alpha subunits and to act merely as a regulatory component for the alpha subunits which regulated the activities of appropriate effectors. However, recent studies have revealed that betagamma subunits dissociated from G protein trimers are also capable of directly regulating the activity of various effectors, such as adenylyl cyclase, K^+ channel, and phospholipase C.Moreover, the betagamma subunits appear to interact with cytoplasmic proteins such as phosducin and beta-adrenergic receptor kinase other than receptors or effectors.
In the present studies, we purified the betagamma subunits of G proteins from bovine brain membranes and found that there were chromatographically multiple forms of betagamma subunits which could be reassociated with various alpha-subunits. We also investigated cytosolic proteins that might interact with the betagamma subunits by means of betagamma subunit-immobilized affinity-column chromatography (betagamma-immobilized column). One of proteins purified through the beta-immobilized column had molecular weight of 93,000. The 93-kDa betagamma-binding protein appeared to be present in many tissues and identified as heat shock protein, hsp90. The hsp90 inhibited beta-supported pertussis toxin-catalyzed ADP-ribosylation of alpha subunits. The hsp90 was also capable of binding to betagamma subunits which had been reconstituted into phospholipid vesicles. The binding of hsp90 to betagamma subunits was inhibited by the addition of GDP-bound alpha subunits, but not by GTPgammaS-bound ones. These results suggested that hsp90 could associate functionally with free betagamma subunits dissociated from trimeric G proteins.
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