2015 Fiscal Year Annual Research Report
Exploring the structure and mechanism of formation of an artificial protein capsid, toward the development of a novel redox-responsive nano-carrier system.
|Research Institution||Institute of Physical and Chemical Research |
Malay Ali 国立研究開発法人理化学研究所, 環境資源科学研究センター, 研究員 (40467006)
|Project Period (FY)
2013-04-01 – 2016-03-31
|Keywords||protein cage / bionanotechnology / gold cluster / gold chemistry / self assembly / capsid / protein engineering / coordination chemistry|
|Outline of Annual Research Achievements
This year's results can be summarized into two main themes:
Structure: the structure of the artificial protein cage "TRAP-cage" has been elucidated via cryoelectron microscopy. The architecture and symmetry of the cage structure is unique among natural or designed protein cages. In summary, the hollow cage consists of 24 cysteine-mutated TRAP rings, corresponding to 264 subunits in total (approximately 2.2 megadaltons). Despite the C11 symmetry of the rings, the cage itself has full octahedral symmetry -- the apparent discrepancy can be explained using the "symmetrohedra" concept.
Mechanism: The rings in the TRAP-cage are held together by the coordination of gold atoms, via the mutated cysteine residues in TRAP rings. A model for the chemistry behind cage assembly is proposed. Addition of Au55 cluster to thiolated ring protein induces the dissociation of Au(+1) ions, which leads to the formation of linear S-Au-S coordination complexes. The eventual self-assembly of the cages, theoretically having 120 such coordination bonds, was tracked using transmission electron microscopy. The proposed mechanism has been confirmed using the gold-based drug auranofin to induce TRAP-cage assembly.
Overall, the results suggests a novel and inducible method for building large, supramolecular protein cages, not limited by platonic geometry or the principles of viral quasi-equivalence. The results are being prepared for publication (target journal: Nature).