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Helical Secondary Structure (helical + secondary_structure)
Selected AbstractsChemInform Abstract: Stereospecific Synthesis of Conformationally Constrained ,-Amino Acids: New Foldamer Building Blocks That Support Helical Secondary Structure.CHEMINFORM, Issue 10 2010Li Guo Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Stepwise proteolytic removal of the , subdomain in ,-lactalbuminFEBS JOURNAL, Issue 15 2001The protein remains folded, can form the molten globule in acid solution Bovine ,-lactalbumin (,-LA) is an ,/, protein which adopts partly folded states when dissolved at low pH (A-state), by removal of the protein-bound calcium at neutral pH and low salt concentration (apo-state), as well as in aqueous trifluoroethanol. Previous spectroscopic studies have indicated that the A-state of ,-LA at pH 2.0, considered a prototype molten globule, has a native-like fold in which the helical core is mostly retained, while the , subdomain is less structured. Here, we investigate the conformational features of three derivatives of ,-LA characterized by a single peptide bond fission or a deletion of 12 or 19/22 amino-acid residues of the , subdomain of the native protein (approximately from residue 34 to 57). These ,-LA derivatives were obtained by limited proteolysis of the protein in its partly folded state(s). A nicked ,-LA species consisting of fragments 1-,3,40 and 41,123 (nicked-LA) was prepared by thermolytic digestion of the 123-residue chain of ,-LA in 50% (v/v) aqueous trifluoroethanol. Two truncated or gapped protein species given by fragments 1,40 and 53,123 (des,1-LA) or fragments 1,34 and 54-,57,123 (des,2-LA) were obtained by digestion of ,-LA with pepsin in acid or with proteinase K at neutral pH in its apo-state, respectively. The two protein fragments of nicked or gapped ,-LA are covalently linked by the four disulfide bridges of the native protein. CD measurements revealed that, in aqueous solution at neutral pH and in the presence of calcium, the three protein species maintain the helical secondary structure of intact ,-LA, while the tertiary structure is strongly affected by the proteolytic cleavages of the chain. Temperature effects of CD signals in the far- and near-UV region reveal a much more labile tertiary structure in the ,-LA derivatives, while the secondary structure is mostly retained even upon heating. In acid solution at pH 2.0, the three ,-LA variants adopt a conformational state essentially identical to the molten globule displayed by intact ,-LA, as demonstrated by CD measurements. Moreover, they bind strongly the fluorescent dye 8-anilinonaphthalene-1-sulfonate, which is considered a diagnostic feature of the molten globule of proteins. Therefore, the , subdomain can be removed from the ,-LA molecule without impairing the capability of the rest of the chain to adopt a molten globule state. The results of this protein dissection study provide direct experimental evidence that in the ,-LA molten globule only the , domain is structured. [source] Thermal denaturation pathway of starch phosphorylase from Corynebacterium callunae: Oxyanion binding provides the glue that efficiently stabilizes the dimer structure of the proteinPROTEIN SCIENCE, Issue 6 2000Richard GrießLer Abstract Starch phosphorylase from Corynebacterium callunae is a dimeric protein in which each mol of 90 kDa subunit contains 1 mol pyridoxal 5,-phosphate as an active-site cofactor. To determine the mechanism by which phosphate or sulfate ions bring about a greater than 500-fold stabilization against irreversible inactivation at elevated temperatures (,50°C), enzyme/oxyanion interactions and their role during thermal denaturation of phosphorylase have been studied. By binding to a protein site distinguishable from the catalytic site with dissociation constants of Ksulfate = 4.5 mM and Kphosphate,16 mM, dianionic oxyanions induce formation of a more compact structure of phosphorylase, manifested by (a) an increase by about 5% in the relative composition of the ,-helical secondary structure, (b) reduced 1H/2H exchange, and (c) protection of a cofactor fluorescence against quenching by iodide. Irreversible loss of enzyme activity is triggered by the release into solution of pyridoxal 5,-phosphate, and results from subsequent intermolecular aggregation driven by hydrophobic interactions between phosphorylase subunits that display a temperature-dependent degree of melting of secondary structure. By specifically increasing the stability of the dimer structure of phosphorylase (probably due to tightened intersubunit contacts), phosphate, and sulfate, this indirectly (1) preserves a functional active site up to, 50°C, and (2) stabilizes the covalent protein cofactor linkage up to , 70°C. The effect on thermostability shows a sigmoidal and saturatable dependence on the concentration of phosphate, with an apparent binding constant at 50°C of , 25 mM. The extra stability conferred by oxyanion-ligand binding to starch phosphorylase is expressed as a dramatic shift of the entire denaturation pathway to a , 20°C higher value on the temperature scale. [source] Melectin: A Novel Antimicrobial Peptide from the Venom of the Cleptoparasitic Bee Melecta albifronsCHEMBIOCHEM, Issue 17 2008Václav, ovskı Dr. Abstract A novel antimicrobial peptide designated melectin was isolated from the venom of the cleptoparasitic bee Melecta albifrons. Its primary sequence was established as H-Gly-Phe-Leu-Ser-Ile-Leu-Lys-Lys-Val-Leu-Pro-Lys-Val-Met-Ala-His-Met-Lys-NH2 by Edman degradation and ESI-QTOF mass spectrometry. Synthetic melectin exhibited antimicrobial activity against both Gram-positive and -negative bacteria and it degranulated rat peritoneal mast cells, but its hemolytic activity was low. The CD spectra of melectin measured in the presence of trifluoroethanol and sodium dodecyl sulfate showed a high content ,-helices, which indicates that melectin can adopt an amphipathic ,-helical secondary structure in an anisotropic environment such as the bacterial cell membrane. To envisage the role of the proline residue located in the middle of the peptide chain on biological activity and secondary structure, we prepared several melectin analogues in which the Pro11 residue was either replaced by other amino acid residues or was omitted. The results of biological testing suggest that a Pro kink in the ,-helical structure of melectin plays an important role in selectivity for bacterial cells. In addition, a series of N- and C-terminal-shortened analogues was synthesized to examine which region of the peptide is related to antimicrobial activity. [source] The Influence of Surface Composition of Nanoparticles on their Interactions with Serum AlbuminCHEMPHYSCHEM, Issue 14 2010Dr. Lennart Treuel Abstract Interactions between differently functionalised silver and gold nanoparticles (NPs) as well as polystyrene nanoparticles with bovine serum albumin (BSA) are studied using circular dichroism (CD) spectroscopy. It is found that the addition of NPs to the protein solution destroys part of the helical secondary structure of the protein as a result of surface adsorption. From the loss of free protein and hence the extent of their structural change adsorption equilibrium constants are derived. The results reveal that citrate-coated gold and silver NPs exhibit much stronger interactions with BSA than polymeric or polymer-coated metallic NPs. It is therefore concluded that for the particles considered, the influence of surface composition on the interaction behaviour dominates that of the core. [source] Synthesis, and Structural and Biological Studies of Efrapeptin C AnaloguesCHEMISTRY & BIODIVERSITY, Issue 6 2007Micha Jost Abstract A series of analogues of efrapeptin,C (1), with variations in the central tripeptide epitope (positions 6,8), were prepared by a combination of solid- and solution-phase peptide syntheses. The conformations of the modified compounds 2,6 were investigated by circular-dichroism (CD) spectroscopy to differentiate between 310 - and , -helical secondary structures. The inhibitory activities of the new compounds towards F1 -ATPase from E. coli were determined. The modified congeners 3,5 were less active by one order of magnitude compared to 1 (Ki 10,,M), and 6 was completely inactive. Our experiments demonstrate that the flexible, central tripeptide epitope, comprising positions 6,8 in 1, is crucial for molecular recognition, even slight sequence modifications being hardly tolerated. [source] Conformation and Interaction of a d,l -Alternating Peptide with a Bilayer Membrane: X-ray Reflectivity, CD, and FTIR Spectroscopy,CHEMPHYSCHEM, Issue 16 2007Andrea Küsel Dr. Abstract Peptides with alternating amino acid configuration provide helical secondary structures that are especially known from the membrane channel and pore-forming gramicidin A. In analogy to this natural d,l- alternating pentadecapeptide, the potential of d,l- alternating peptides for membrane insertion is investigated using the model dodecamer peptide H -(Phe- Tyr)5 -Trp- Trp - OH. This aromatic peptide is introduced as a novel pore-forming synthetic analogue of gramicidin A. It forms a well-organized homodimer similar to one of the gramicidin A transmembrane motifs. X-ray reflectivity measurements are performed on solid-supported peptide,lipid complexes to obtain information about the influence of the artificial dodecamer peptide on the bilayer parameters. In addition, Fourier-transform infrared (FTIR) and circular dichroism (CD) spectroscopic studies determine the conformational state of H -(Phe- Tyr)5 -Trp- Trp - OH within the model membrane. Site-specific iodine labeling assists in determining the topology of the membrane-embedded peptide by pinpointing the position of the iodine label within the bilayers. [source] | ||||||||||