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Division of Materials Science |
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Biochemistry Group
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Toshiya Endo Professor |
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Toshiya Endo (Professor)
Life of proteins and organelle biogenesis
Tohru Yoshihisa (Associate Professor)
Intracellular dynamics of tRNA during its biogenesis
Shuh-ichi Nishikawa (Associate Professor)
Control of organelle formation and organelle biogenesis
by molecular chaperones
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Life of proteins and cellular functions
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Proteins are major key players in the living systems and their
amino-acid sequences are controlled by the genetic information in
DNA. Newly synthesized proteins need to fold into their native conformations
to become functional. However, recent evidence shows that this process
is not spontaneous, but requires helper proteins called molecular
chaperones in cells.
Eukaryotic cells contain various membrane-bounded compartments or
organelles, and by virtue of this compartmentalization, they can perform
complex reactions in parallel in distinct compartments, store energy
by distributing substances asymmetrically to the organellar membranes
etc. To perform their functions, organelles need to place resident
proteins in correct intraorganellar locations. Cells thus employ protein
translocators in the organellar membranes and soluble molecular chaperones,
which control the protein traffic and deliver newly synthesized proteins
to the appropriate destination compartments. The protein translocators
are protein nano-machines that perform multiple tasks; they function
as receptors for targeting signals, provides a protein-conducting
channel through which newly synthesized proteins cross the organellar
membrane in an unfolded state, and offer a driving force to achieve
vectorial movement of the translocating polypeptide chain. Much recent
interest is focused on how the translocators perform these complex
functions correctly and efficiently.
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| Fig. Translocators controlling mitochondrial
protein import. |
Even after folding into their native structures at the appropriate
destination compartments, some proteins may become nonfunctional due
to stresses placed on cells, such as high temperature, exposure to
heavy metals, oxidative stresses etc. In these cases, various types
of molecular chaperones are utilized to repair the aberrant proteins.
If efforts to renature proteins fail, the aberrant proteins are subjected
to disposal by degradation systems. Central questions remaining to
be answered include how the cell discriminate between normal and aberrant
proteins and how the final judgment on protein fate is made. It also
remains vague if the protein quality control has profound biological
significance at the level of multicellular organisms such as fertilization
and development of higher plants.
We are making every effort to address questions on the various aspects
of the life of proteins listed up above by using variety of techniques
including biochemistry, molecular biology, cell biology, structural
biology, and genetics.
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| Members of the Endo Lab. |
We are also extending our analyses of intracellular
traffic and quality control to the life of RNAs in eukaryotic cells.
We are thus trying to envision a new picture of proteins (and RNAs)
in the context of a dynamic cellular environment.
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References
- Sato, T. et al. (2005) Proc. Natl. Acad. Sci. USA 102: 17999-18004
- Takano, A. et al. (2005) Science 309: 140-142
- Ishikawa, D. et al. (2004) J. Cell Biol. 166: 621-627
- Esaki, M. et al. (2003) Nature Struct. Biol. 10: 988-994
- Endo, T. et al. (2003) J. Cell Sci. 116: 3259-3267
- Yamamoto, H. et al. (2002) Cell 111: 519-52
- Nishikawa, S. et al. (2001) J. Cell Biol. 153: 1061-1070
- Abe, Y. et al. (2000) Cell 100: 551-560
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i n d e x |
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 Biochemistry
Group
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Molecular
Neurobiology Group