120105 - BE.342/442 Thursday, December, 2005 Topic: Prof....

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BE.342/442 Thursday, December, 2005 Topic: Prof. Zhang’s Research and Guest Lecture by Andreas Mershin: “Applying Biomimicry to Nanotechnology.” Administrative Take-home midterms will be returned next Tuesday. Stabilization of membrane proteins with detergents (Continued from last time.) Structure of bovine rhodopsin: transformation in optical properties in photo cycle. Two distinctive absorptions are observed in bovine rhodopsin: in the dark, near 500 nm, and under light, at 380 nm. Heating, as well as illumination, changes the relative ratios of the absorbance peaks at these two frequencies. Rhodopsin tends to degrade over time. Detergents such as A6D and DM can stabilize the protein to some extent, but many require cold temperatures to impart stability. A6D alone can stabilize the protein at 55°C for more than 11 hours. Discovery of new detergents could be critical to further study of membrane proteins. Without stabilization by detergents, membrane proteins tend to aggregate out of solution due to the driving force for hydrophobic bonding in their nonpolar regions, which are normally embedded in membranes. Detergents can coat these regions with their hydrophobic tails, presenting hydrophilic head groups to the solvent and stabilizing the protein in its native conformation. Joanne Yeh and co-workers used A6DA6K with 200 mM NaCl and OG with 200 mM NaCl to stabilize a matrix protein and allow it to crystallize. Source: Joanne I. Yeh et al, “Peptergents: Peptide Detergents that Improve Stability and Functionality of a Membrane Protein, Glycerol-3-Phosphate Dehydrogenase.” Biochemistry , 2005 (in press). Prof. Zhang looked into 3-D membrane lattices with membranes linked by bridging proteins into a stack. The proteins set the distance between the membranes, and can be made to bend the proteins. These structures could prove useful for membrane protein stabilization. Alpha-helical Materials Andreas Lomander and colleagues attempted to create an alpha helical molecular switch, in which gold nanoparticles are coupled to the ends to two alpha helices (a coiled coil) by Cys residues. Although this strategy did not work out directly, the work did lead to formation of fractal patters of gold on mica. With an enormous surface area, the branching gold structure resembles the leaves of a fern.
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Using simulations, they discovered that the coiled coils coupled to each other by disulfide bridges, forming a cross-shaped structure with no more than six pairs. The structures of six coiled-coils likely formed clusters that deposited into the mica substrate at low pH (at least, this is the theory; this has not been proven). Experiments using hydrophobic denaturant (DTT and beta-mercaptoethanol) to separate the alpha-helices of the coiled
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120105 - BE.342/442 Thursday, December, 2005 Topic: Prof....

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