Toward Catalytic Nano-Bioreactor Based on Highly Thermostable Spherical Protein
Written by Sivan Avihasira
S. Avihasiraa, A. Pogoreltseva, D. Pappoa and E. Keinana,b
aThe Schulich Faculty of Chemistry and Institute of Catalysis Science and Technology, Technion – Israel Institute of Technology Technion City, Haifa 32000, Israel.
bDepartments of Molecular Biology and Cell Biology, and the Skaggs Inst. of Chemical Biology, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
The heat shock proteins (HSPs) are a highly conserved family of stress response proteins. HSPs are expressed at low levels under normal physiological conditions but show dramatically increased expression in response to cellular stress, including high and low temperatures, salinity and oxidative stress. We plan to focus on sHSP16.5, which was originally isolated from Methanococcus jannaschii, a hyperthermophilic archaeon. The sHSP16.5 comprises 24 monomeric units that form a hollow spherical complex of octahedral symmetry with eight triagonal and six square windows on its surface. Each monomeric folding unit, consist of 147 amino acids, contains partially disordered N-terminus (the first 32 amino acids) which appear to be inside the sphere. The outer and inner diameters of the hollow sphere are 120Å and 65Å, respectively .we plan to modify the sHSP in such away that it will contain amino acids that have high affinity to metals in its interior. The chirality of the self assembled modified sHSP 16.5 can facilitate asymmetric chemical reactions with coordinated metal ions.
We plan to insert into the synthetic N-terminal domain at least one residue with metal reduction/nucleation property, that would facilitate reduction of metal ions, such as silver, and nucleation of a metallic nano-particle within the cavity of the modified HSP16.5 sphere. There are two main goals: 1) Creation of catalytic nano-reactors in which the catalytic metal centers are confined within the hollow sphere while the starting materials and products traveling back and forth from the bulk solvent to the reactor cavity through large portals in the sphere. This technology will allow homogeneous metal-catalysis, and asymmetric catalysis in particular, with the advantages that are usually associated with heterogeneous catalysis. 2) Generation of uniform core-shell nanoparticles through controlled nucleation and limited growth of a metallic core inside the protein shell. Such confined metallo-nanoparticles will be used as chemically addressable electron-dense labeling devices for electron microscopy and for the generation of nanoparticles arrays.