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91.
Controlling the DNA binding specificity of bHLH proteins through intramolecular interactions 总被引:2,自引:0,他引:2
Reversible control of the conformation of proteins was employed to probe the relationship between flexibility and specificity of the basic helix-loop-helix protein MyoD. A fusion protein (apaMyoD) was designed where the basic DNA binding helix of MyoD was stablized by an amino-terminal extension with a sequence derived from the bee venom peptide apamin. The disulfide-stabilized helix from apamin served as a nucleus for a helix that extended for a further ten residues, thereby holding apaMyoD's DNA recognition helix in a predominantly alpha-helical conformation. The thermal stability of the DNA complexes of apaMyoD was increased by 13 degrees C relative to MyoD-bHLH. Measurements of the fluorescence anisotropy change on DNA binding indicated that apaMyoD bound to E-box-containing DNA sequences with enhanced affinity relative to MyoD-bHLH. Consequently, the DNA binding specificity of apaMyoD was increased 10-fold. 相似文献
92.
Grald Lelais Dieter Seebach Bernhard Jaun RaveendraI. Mathad Oliver Flgel Francesco Rossi Marino Campo Arno Wortmann 《Helvetica chimica acta》2006,89(3):361-403
The correlation between β2‐, β3‐, and β2,3‐amino acid‐residue configuration and stability of helix and hairpin‐turn secondary structures of peptides consisting of homologated proteinogenic amino acids is analyzed (Figs. 1–3). To test the power of Zn2+ ions in fortifying and/or enforcing secondary structures of β‐peptides, a β‐decapeptide, 1 , four β‐octapeptides, 2 – 5 , and a β‐hexadecapeptide, 10 , have been devised and synthesized. The design was such that the peptides would a) fold to a 14‐helix ( 1 and 3 ) or a hairpin turn ( 2 and 4 ), or form neither of these two secondary structures (i.e., 5 ), and b) carry the side chains of cysteine and histidine in positions, which will allow Zn2+ ions to use their extraordinary affinity for RS? and the imidazole N‐atoms for stabilizing or destabilizing the intrinsic secondary structures of the peptides. The β‐hexadecapeptide 10 was designed to a) fold to a turn, to which a 14‐helical structure is attached through a β‐dipeptide spacer, and b) contain two cysteine and two histidine side chains for Zn complexation, in order to possibly mimic a Zn‐finger motif. While CD spectra (Figs. 6–8 and 17) and ESI mass spectra (Figs. 9 and 18) are compatible with the expected effects of Zn2+ ions in all cases, it was shown by detailed NMR analyses of three of the peptides, i.e., 2, 3, 5 , in the absence and presence of ZnCl2, that i) β‐peptide 2 forms a hairpin turn in H2O, even without Zn complexation to the terminal β3hHis and β3hCys side chains (Fig. 11), ii) β‐peptide 3 , which is present as a 14‐helix in MeOH, is forced to a hairpin‐turn structure by Zn complexation in H2O (Fig. 12), and iii) β‐peptide 5 is poorly ordered in CD3OH (Fig. 13) and in H2O (Fig. 14), with far‐remote β3hCys and β3hHis residues, and has a distorted turn structure in the presence of Zn2+ ions in H2O, with proximate terminal Cys and His side chains (Fig. 15). 相似文献
93.
Lumbierres M Palomo JM Kragol G Roehrs S Müller O Waldmann H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(24):7405-7415
A new flexible and efficient methodology for the solid-phase synthesis of lipidated peptides has been developed. The approach is based on the use of previously synthesized building blocks and overcomes the limitations of previously reported methods, since long doubly lipidated peptides can be synthesized by using this route. Furthermore, it was thus possible to prepare a large number of N- and H-Ras peptides bearing a wide range of reporter and/or linking groups--efficient tools for the investigation of biological processes. In terms of efficiency and flexibility this solid-phase method is superior to the solution-phase synthesis. It gives pure peptides in multimilligram amounts within a much shorter time and with superior overall yield. 相似文献
94.
Petrovic AG Polavarapu PL Drabowicz J Zhang Y McConnell OJ Duddeck H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(14):4257-4262
The enantiomers of 3,3,3',3'-tetramethyl-1,1'-spirobi[3 H,2,1]benzoxaselenole have been separated on a chiral preparative chromatographic column. The experimental vibrational circular dichroism (VCD) spectra have been obtained for both enantiomers in CH(2)Cl(2). The theoretical VCD spectra have been obtained by means of density functional theoretical calculations with the B3 LYP density functional. From a comparison of experimental and theoretical VCD spectra, the absolute configuration of an enantiomer with positive specific rotation in CH(2)Cl(2) at 589 nm is determined to be R. This conclusion has been verified by comparing results of experimental optical rotatory dispersion (ORD) and electronic circular dichroism (ECD) to predictions of the same properties using the B3 LYP functional for the title compound. 相似文献
95.
Many photoactive metal complexes can act as electron donors or acceptors upon photoexcitation, but hydrogen atom transfer (HAT) reactivity is rare. We discovered that a typical representative of a widely used class of iridium hydride complexes acts as an H-atom donor to unactivated olefins upon irradiation at 470 nm in the presence of tertiary alkyl amines as sacrificial electron and proton sources. The catalytic hydrogenation of simple olefins served as a test ground to establish this new photo-reactivity of iridium hydrides. Substrates that are very difficult to activate by photoinduced electron transfer were readily hydrogenated, and structure–reactivity relationships established with 12 different olefins are in line with typical HAT reactivity, reflecting the relative stabilities of radical intermediates formed by HAT. Radical clock, H/D isotope labeling, and transient absorption experiments provide further mechanistic insight and corroborate the interpretation of the overall reactivity in terms of photo-triggered hydrogen atom transfer (photo-HAT). The catalytically active species is identified as an Ir(ii) hydride with an IrII–H bond dissociation free energy around 44 kcal mol−1, which is formed after reductive 3MLCT excited-state quenching of the corresponding Ir(iii) hydride, i.e. the actual HAT step occurs on the ground-state potential energy surface. The photo-HAT reactivity presented here represents a conceptually novel approach to photocatalysis with metal complexes, which is fundamentally different from the many prior studies relying on photoinduced electron transfer.Upon irradiation with visible light, an iridium hydride complex undergoes hydrogen atom transfer (HAT) to unactivated olefins in presence of a sacrificial electron donor and a proton source. 相似文献
96.
Masood Parvez Oliver E. Edwards Zdzisaw Paryzek 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(4):o249-o251
The structures of 3β‐acetoxy‐9α,11α‐epoxy‐5α‐lanost‐9(11)‐en‐7‐one and 3β‐acetoxy‐9β,11β‐epoxy‐5α‐lanost‐9(11)‐en‐7‐one, C32H52O4, differ in their respective substituted cyclohexanone rings but adopt similar conformations in the other three rings. In both of the crystal structures, weak intermolecular C—H⋯O interactions are present. 相似文献
97.
Oliver Tietze Birgit Schiefner Burkhard Ziemer A. Zschunke 《Analytical and bioanalytical chemistry》1997,357(5):477-481
The reaction of ethylenediamine with an equivalent mixture of diversely substituted 3-acyltetramic acids leads to Z/Z, Z/E,
E/Z and E/E isomers. The E/Z isomerisation is slow in the NMR time scale of the 1H and 13C chemical shifts; therefore at room temperature and in deuterochloroform all isomers of the new synthesized asymmetric compounds
N,N′-ethylene-(1-ethyl-5,5-dimethyl-1′,5′,5′-trimethyl-3,3′-acetyltetramic acid) a, N,N′-ethylene-(5,5-dimethyl-1′,5′,5′-trimethyl-3,3′-acetyltetramic
acid) b and, N,N′-ethylene-(1,5,5-trimethyl-1′,5′,5′-trimethyl-3-acetyl-3′-formyl-tetramic acid) c could be found in the corresponding
spectra. To assign the 13C NMR signals we used two-dimensional 13C-1H one-bond (HMQC) and 13C-1H multibond (HMBC) correlated spectroscopy and the empirical rule that CO signals involved in hydrogen bonds are shifted to
a lower field. The relative stability of isomers depending on substitution pattern could be estimated from the composition
of the equilibria. b crystallizes as Z/Z isomer from ethanolic solution. The X-ray structural analysis of b has shown two
CH-O hydrogen bonds.
Received: 31 May 1996 / Revised: 26 June 1996 / Accepted: 1 July 1996 相似文献
98.
Galvanic cells of the type (C+Cl2)(NaCl(s))(MCl2(s))(C+Cl2) give e. m. f. 's above 280°, which are due to the formation of ternary chlorides NanMCln+2. By the change in slope of continuously measured e.m.f.vs. T curves, the temperatures of solid-state reactions in systems NaCl-MCl2 can be found. This method was applied for the systems of NaCl with NiCl2, CoCl2 and CdCl2, and for KCl-NiCl2. With the exception of the system NaCl-NiCl2, all phase diagrams must be corrected.
This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. 相似文献
Zusammenfassung Mit galvanischen Zellen des Typs (C+Cl2)/NaCl(s)/MCl2(s)/(C+Cl2) lassen sich oberhalb 280° EMK's messen, die auf der Bildung ternärer Chloride NanMCln+2 beruhen. Durch die Änderung der Steigung kontinuierlich gemessener EMK- gegen T-Kurven lassen sich in Systemen NaCl/MCl2 die Temperaturen von Festkörperreaktionen nachweisen. Diese Methode wurde auf die Systeme des NaCl mit NiCl2, CoCl2 und CdCl2 sowie auf das System KCl-NiCl2 angewendet. Alle Phasendiagramme, mit Ausnahme des Systems NaCl-NiCl2, mußten auf Grund dieser Messungen revidiert werden.
(C+Cl2)/NaCl./MCl2./(C +Cl2) 280 °C . . , NanMCln+2. . . , NaCl-MCl2. NaCl NiCl2, CoCl2, CdCl2 KCl-NiCl2. NaCl-NiCl2,ce .
This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. 相似文献
99.
The stability of the molecular host-guest inclusion complexes of beta-cyclodextrin with benzoate and four different hydroxybenzoates is investigated. For the measurement of the binding constants an experimental method is devised that is based on affinity capillary electrophoresis (ACE) with indirect UV absorbance detection. We derive an explicit equation for effective mobilities in ACE experiments without violation of rigorous mass balance. This equation is employed in the nonlinear least-squares analyses of the experimental data yielding binding constants of 48+/-2 M(-1) for benzoate, 299+/-38 M(-1) for 2-hydroxybenzoate, 37+/-1 M(-1) for 3-hydroxybenzoate, 228+/-9 M(-1) for 4-hydroxybenzoate, and 895+/-110 M(-1) in the case of 2,4-dihydroxybenzoate. 相似文献
100.
Napper AM Head NJ Oliver AM Shephard MJ Paddon-Row MN Read I Waldeck DH 《Journal of the American Chemical Society》2002,124(34):10171-10181
A systematic determination of electronic coupling matrix elements in U-shaped molecules is demonstrated. The unique architecture of these systems allows for the determination of the electronic coupling through a pendant molecular moiety that resides between the donor and acceptor groups; this moiety quantifies the efficiency of electron tunneling through nonbonded contacts. Experimental electron-transfer rate constants and reaction free energies are used to calibrate a molecular-based model that describes the solvation energy. This approach makes it possible to experimentally determine electronic couplings and compare them with computational values. 相似文献