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11.
Mia C. Brown Andrew C. Mutter Ronald L. Koder Renee D. JiJi Jason W. Cooley 《Journal of Raman spectroscopy : JRS》2013,44(7):957-962
The molten globule (MG) state can aid in the folding of a protein to a functional structure and is loosely defined as an increase in structural disorder with conservation of the ensemble secondary structure content. Simultaneous observation of persistent secondary structure content with increased disorder has remained experimentally problematic. As a consequence, modeling how the MG state remains stable and how it facilitates proper folding remains difficult due to a lack of amenable spectroscopic techniques to characterize this class of partially unfolded proteins. Previously, deep‐UV resonance Raman (dUVRR) spectroscopy has proven useful in the resolution of global and local structural fluctuations in the secondary structure of proteins. In this work, dUVRR was employed to study the MG to ordered transition of a model four‐helix bundle protein, HP7. Both the average ensemble secondary structure and types of local disorder were monitored, without perturbation of the solvent, pH, or temperature. The MG to ordered transition is induced by stepwise coordination of two heme molecules. Persistent dUVRR spectral features in the amide III region at 1295–1301 and 1335–1338 cm−1 confirm previous observations that HP7 remains predominantly helical in the MG versus the fully ordered state. Additionally, these spectra represent the first demonstration of conserved helical content in a MG protein. With successive heme binding, significant losses are observed in the spectral intensity of the amide III3 and S regions (1230–1260 and 1390 cm−1, respectively), which are known to be sensitive to local disorder. These observations indicate that there is a decrease in the structural populations able to explore various extended conformations with successive heme binding events. DUVRR spectra indicate that the first heme coordination between two helical segments diminishes exploration of more elongated backbone structural conformations in the inter‐helical regions. A second heme coordination by the remaining two helices further restricts protein motion. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
12.
Canoy WL Cooley BE Corona JA Lovelace TC Millar A Weber AM Xie S Zhang Y 《Organic letters》2008,10(6):1103-1106
A one-step diastereoselective (up to 98:2) synthesis of the bis-furan alcohol of Darunavir and other HIV drug candidates has been achieved utilizing the novel cyclization of glycolaldehyde and 2,3-dihydrofuran. The cycloaddition was catalyzed by a variety of catalysts including those formed from tin(II) triflate and common chiral ligands such as BINAP and Evans's box ligands. An efficient and unique enzymatic process enhanced the enantiomeric purity to provide the target in optically pure form. 相似文献
13.
Matthew L. Milling Jermaine Cooley Dmitriy V. Liskin Edward J. Valente 《Structural chemistry》2009,20(6):969-973
Abstract
Oxidation of 1,4-bis(4′-oxo-2′,2′-dimethylpent-2-yl)benzene with hypochlorite produces 1,4-bis(3′-carboxy-2′-methylbut-2-yl)benzene and 3-(4′-carboxyphenyl)-3,3-dimethylpropanoic acid. Cyclization of this mixture forms 3,3,7,7-tetramethyl-1,2,3,5,6,7-hexahydro-s-indacen-1,5-dione, 3,3,7,7-tetramethyl-1,2,3,5,6,7-hexahydro-as-indacen-1,5-dione (5) and 6-carboxy-3,3-dimethyl-1-indanone (6). Ketoacid (6) is converted to the arylpyran pseudoacid 7-carboxy-3-hydroxy-4,4-dimethylisobenzopyran-1-one (7). In the crystal structure of (7), carboxylic acid and the pseudoacid groups each form complementary dimer hydrogen bonds linking the molecules in chains. Contact O···O distances reflect their differing energetics, with pseudoacyl O···O at 2.78(1)Å and carboxylic O···O at 2.62(1)Å. 相似文献14.
The Loebl–Komlós–Sós conjecture states that for any integers k and n, if a graph G on n vertices has at least n/2 vertices of degree at least k, then G contains as subgraphs all trees on k+1 vertices. We prove this conjecture in the case when k is linear in n, and n is sufficiently large. 相似文献
15.
Seitchik JL Peeler JC Taylor MT Blackman ML Rhoads TW Cooley RB Refakis C Fox JM Mehl RA 《Journal of the American Chemical Society》2012,134(6):2898-2901
Bioorthogonal ligation methods with improved reaction rates and less obtrusive components are needed for site-specifically labeling proteins without catalysts. Currently no general method exists for in vivo site-specific labeling of proteins that combines fast reaction rate with stable, nontoxic, and chemoselective reagents. To overcome these limitations, we have developed a tetrazine-containing amino acid, 1, that is stable inside living cells. We have site-specifically genetically encoded this unique amino acid in response to an amber codon allowing a single 1 to be placed at any location in a protein. We have demonstrated that protein containing 1 can be ligated to a conformationally strained trans-cyclooctene in vitro and in vivo with reaction rates significantly faster than most commonly used labeling methods. 相似文献
16.
We present torque magnetization measurements on the quasi-2D heavy fermion superconductor CeCoIn5 at temperatures down to 20 mK and magnetic fields up to 18?T. At orientations with the magnetic field perpendicular to the conducting planes, a prominent vortex lattice peak effect is present at around 0.5H c2. The peak effect gradually disappears upon rotating the field into the plane parallel orientation. We interpret the absence of the peak effect for the plane parallel case as a transformation of the Abrikosov lattice into a Josephson vortex state, favored by the Pauli paramagnetic limit in CeCoIn5 together with the unusually large condensation energy. Additionally, we do not observe flux avalanches as found in organic superconductors and suggest that the complete absence of vortex activity in the plane parallel field orientation is crucial for the formation of Fulde–Ferrell–Larkin–Ovchinnikov superconductivity in CeCoIn5. 相似文献
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Two approaches for decreasing diesel hydrocarbon group-type separation times by normal phase supercritical fluid chromatography (SFC) are compared. Short (10-15 cm) columns with small 3 microm diameter packing are compared with monolithic Chromolith bare silica columns under high carbon dioxide flow rates approaching 5 ml min(-1). Elution times are reduced up to 13-fold on a 10 cm Chromolith column and 7-fold on the short packed columns compared with conventional length columns run at typical flow rates. Short packed columns, with their higher surface area and retention characteristics, offer higher resolutions compared with Chromolith columns. Diesel samples are separated into saturates, mono-, di-, tri-, and polyaromatics in as little as 2 min on a 10 cm packed silica column. Diesel group-type results on a 15 cm titania-silica coupled column compare favorably with results from longer columns. 相似文献