Dr. Takashi Okuno (奥野 貴士 准教授)
Faculty of Science, Yamagata University
(山形大学理学部)
A single-molecule analysis of recognition of ubiquitinated proteins
by the 26S proteasome
The 26S proteasome is a huge protease that is responsible for degradation of polyubiquitinated proteins in the Ubiquitin-Proteasome System (UPS). Correct recognition of polyubiquitin chains by the proteasome is required for selective and rapid degradation of unnecessary proteins in vivo. The proteasome has been considered to recognize a polyubiquitin chain on substrate proteins directly. Recent studies, however, suggest that most polyubiquitinated proteins are mainly recruited to the proteasome through the help of Rad23 or Dsk2. Rad23 is known as a shuttle factor containing ubiquitin-like (UbL) and ubiquitin-associated (UBA) domains. The shuttling reaction regulated by Rad23 has not been directly monitored and the precise mechanism remains unclear. In this study, we tried to reveal the recognition mechanism of substrate proteins by Rad23 using single-molecule analysis techniques, Total Internal Reflection Fluorescence Microscopy (TIRFM) and Atomic Force Microscopy (AFM).
Dr. Masaki Okumura (奥村 正樹 助教)
Frontier Research Institute for Interdisciplinary Sciences,
Tohoku University
(東北大学学際科学フロンティア研究所)
Dynamic assembly and disassembly of protein disulfide isomerase
in catalysis of oxidative protein folding
Protein disulfide isomerase (PDI) is the most versatile catalyst of oxidative protein folding, which has research history of more than 50 years. Whereas a number of scientists have so far studied on structures, redox properties and physiological functions of PDI, nobody has succeeded in direct observation for actions of PDI. Recently, we succeeded in direct visualization of PDI engaged in the catalysis of oxidative folding using high-speed AFM. Oxidized PDI acts on unstructured substrates in a highly dynamic fashion at the initial folding, whereas the closed conformation of reduced PDI recognizes relatively compact and structured folding intermediates at later stages. Importantly, only oxidized PDI undergoes repeated cycles of assembly into dimers and disassembly into monomers in the presence of substrates along their folding pathways. However, the PDI dimers are diverse in shape and have different lifetimes, in accordance with sizes, configurations, and folding states and rates, of substrates. Based on these findings, we discuss a new mechanism by which PDI guides substrate folding.
おふたりの演者は、今年度「発生医学の研究拠点」事業の共同研究課題に採択されています。
多数のご来聴を歓迎します。
連絡先：分子細胞制御分野 小椋 光（内線6578）
