Ein Plätzchen zum Kuppeln: Proteine wie das gelb fluoreszierende Protein (YFP), die ein N‐terminales FGG‐Motiv tragen, dimerisieren unter Mitwirkung von supramolekularen Wechselwirkungen innerhalb des Cucurbit[8]uril‐Rings (siehe Schema). Die durch FRET und Größenausschlusschromatographie beobachtbare Dimerisierung lässt sich durch Zugabe von Methylviologen umkehren, das als bioorthogonaler Ligand die FGG‐Motive aus dem Cucurbit[8]uril‐Wirt verdrängt.
A supramolecular protein tetramerization approach has been devised which enables the controlled formation of a discrete protein tetramer. The supramolecular element cucurbit[8]uril has been used as an inducer of the protein tetramerization in combination with intrinsic affinities between the proteins, which preorganize the protein in dimerized form. The combination of a dimerizing interface on the fluorescent proteins under study (dYFP, dCFP), with a genetically encoded N-terminal phenylalanineglycine-glycine (FGG) peptide motif allows cucurbit[8]uril to selectively induce FGG-dYFP or FGG-dCFP tetramerization. The concept of cucurbit[8]uril-induced protein tetramerization was elucidated by using a combination of fluorescence anisotropy, dynamic light scattering and size exclusion chromatography experiments. The cucurbit[8]uril-induced tetrameric protein complex is formed via a ''dimers of dimers'' pathway, is highly stable and can be separated by size exclusion chromatography. This supramolecular induced protein tetramerization approach opens up a novel entry in generating well-defined synthetic protein assemblies.
Hosted dimerization: Proteins such as yellow fluorescent protein (YFP) with an N‐terminal FGG peptide motif form dimers mediated by supramolecular interactions with cucurbit[8]uril (see scheme). The protein dimerization, which is observed by FRET and size‐exclusion chromatography, can be reversed with methyl viologen as a bioorthogonal ligand, which displaces the FGG motifs from the cucurbit[8]uril host.
At the double: Cucurbit[8]uril‐mediated protein dimerization enables reversible control over strong enzyme activation of caspases. Simple addition of a short N‐terminal FGG motif allows for a supramolecular‐mediated 50‐fold enhancement of caspase‐9 catalytic activity.
The low solubility of sugars has hampered the lipase-catalyzed synthesis of fatty acid sugar esters in organic solvents and ionic liquids (ILs), because several solvents that are able to effectively dissolve sugars are detrimental to enzymes. In this work, in order to prepare a high concentration of sugars in ILs, we have developed a new procedure that entails mixing an aqueous sugar solution into ILs followed by removal of the water from the solution. The glucose concentrations in the supersaturated [Emim][TfO] and [Bmim][TfO] were 19 and 10 times higher, respectively, than the solubilities (6.1 and 4.8 g/L) of glucose in the ILs at 25 degrees C. Furthermore, the supersaturated glucose solutions in ILs were maintained over a long period of time without any significant loss of glucose. In ILs that were extremely supersaturated with glucose, lipase-catalyzed esterifications of glucose with vinyl laurate, and lauric acid were successfully carried out. The conversion increased from 8% to 96% at 1 day of reaction by using supersaturated solution in [Bmim][TfO] which had dissolved glucose concentration of 400% higher than its solubility, compared with the reaction using saturated glucose solution. By making the glucose concentration in ILs much higher than the solubility through our novel and simple method, the initial rate and conversion of the lipase-catalyzed reaction were significantly improved.
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