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Detergent Micelles (detergent + micelle)
Selected AbstractsNanodisks protect amphotericin B from ultraviolet light and oxidation-induced damagePEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 6 2009Megan L Tufteland Abstract BACKGROUND: Macrolide polyene antibiotics possess potent broad-spectrum antifungal properties. Use of these agents in the field or in controlled environments is impeded by their poor water solubility and susceptibility to oxidation- and/or light-induced degradation. While typically used for human disease therapy, there is potential to expand the utility of polyene macrolide antibiotics, such as amphotericin B, for control of fungal disease infestation in agricultural settings. Thus, the susceptibility of this antibiotic to exposure-induced activity loss was evaluated. RESULTS: Incubation of the prototype polyene amphotericin B (AMB) with phospholipid vesicles and apolipoprotein A-I results in the formation of nanoscale complexes, termed nanodisks (NDs), capable of solubilizing significant quantities of AMB. To evaluate whether AMB incorporation into NDs conferred protection against light- or oxidation-induced damage, yeast growth inhibition assays were conducted. Compared with AMB solubilized in detergent micelles, AMB incorporated into NDs was protected from damage caused by exposure to UV light as well as by KMnO4 -induced oxidation. Furthermore, AMB-NDs inhibited growth of the turfgrass fungus Marasmius oreades Fr. CONCLUSION: Results suggest that this water-soluble formulation of a natural, biodegradable, antifungal agent represents a potential cost-effective, non-toxic and environmentally friendly substitute for chemical agents currently employed to control a range of fungal infestations. Copyright © 2009 Society of Chemical Industry [source] The oligomeric state and stability of the mannitol transporter, EnzymeIImtl, from Escherichia coli: A fluorescence correlation spectroscopy studyPROTEIN SCIENCE, Issue 8 2006Gertjan Veldhuis Abstract Numerous membrane proteins function as oligomers both at the structural and functional levels. The mannitol transporter from Escherichia coli, EnzymeIImtl, is a member of the phosphoenolpyruvate-dependent phosphotransferase system. During the transport cycle, mannitol is phosphorylated and released into the cytoplasm as mannitol-1-phosphate. Several studies have shown that EIImtl functions as an oligomeric species. However, the oligomerization number and stability of the oligomeric complex during different steps of the catalytic cycle, e.g., substrate binding and/or phosphorylation of the carrier, is still under discussion. In this paper, we have addressed the oligomeric state and stability of EIImtl using fluorescence correlation spectroscopy. A functional double-cysteine mutant was site-specifically labeled with either Alexa Fluor 488 or Alexa Fluor 633. The subunit exchange of these two batches of proteins was followed in time during different steps of the catalytic cycle. The most important conclusions are that (1) in a detergent-solubilized state, EIImtl is functional as a very stable dimer; (2) the stability of the complex can be manipulated by changing the intermicellar attractive forces between PEG-based detergent micelles; (3) substrate binding destabilizes the complex whereas phosphorylation increases the stability; and (4) substrate binding to the phosphorylated species partly antagonizes the stabilizing effect. [source] Expression, purification, and characterization of Thermotoga maritima membrane proteins for structure determinationPROTEIN SCIENCE, Issue 5 2006Linda Columbus Abstract Structural studies of integral membrane proteins typically rely upon detergent micelles as faithful mimics of the native lipid bilayer. Therefore, membrane protein structure determination would be greatly facilitated by biophysical techniques that are capable of evaluating and assessing the fold and oligomeric state of these proteins solubilized in detergent micelles. In this study, an approach to the characterization of detergent-solubilized integral membrane proteins is presented. Eight Thermotoga maritima membrane proteins were screened for solubility in 11 detergents, and the resulting soluble protein,detergent complexes were characterized with small angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR) spectroscopy, circular dichroism (CD) spectroscopy, and chemical cross-linking to evaluate the homogeneity, oligomeric state, radius of gyration, and overall fold. A new application of SAXS is presented, which does not require density matching, and NMR methods, typically used to evaluate soluble proteins, are successfully applied to detergent-solubilized membrane proteins. Although detergents with longer alkyl chains solubilized the most proteins, further characterization indicates that some of these protein,detergent complexes are not well suited for NMR structure determination due to conformational exchange and protein oligomerization. These results emphasize the need to screen several different detergents and to characterize the protein,detergent complex in order to pursue structural studies. Finally, the physical characterization of the protein,detergent complexes indicates optimal solution conditions for further structural studies for three of the eight overexpressed membrane proteins. [source] Trifluoroethanol and binding to model membranes stabilize a predicted turn in a peptide corresponding to the first extracellular loop of the angiotensin II AT1A receptorBIOPOLYMERS, Issue 1 2002Roberto K. Salinas Abstract Homology modeling of the angiotensin II AT1A receptor based on rhodopsin,s crystal structure has assigned the 92,100 (YRWPFGNHL) sequence of the receptor to its first extracellular loop. Solution and membrane-bound conformational properties of a peptide containing this sequence (EL1) were examined by CD, fluorescence, and 1H-NMR. CD spectra in aqueous solution revealed an equilibrium between less organized and folded conformers. NMR spectra indicated the coexistence of trans and cis isomers of the Trp3,Pro4 bond. A positive band at 226 nm in the CD spectra suggested aromatic ring stacking, modulated by EL1's ionization degree. CD spectra showed that trifluoroethanol (TFE), or binding to detergent micelles and phospholipid bilayers, shifted the equilibrium toward conformers with higher secondary structure content. Different media gave rise to spectra suggestive of different ,-turns. Chemical shift changes in the NMR spectra corroborated the stabilization of different conformations. Thus, environments of lower polarity or binding to interfaces probably favored the formation of hydrogen bonds, stabilizing ,-turns, predicted for this sequence in the whole receptor. Increases in Trp3 fluorescence intensity and anisotropy, blue shifts of the maximum emission wavelength, and pK changes also evinced the interaction between EL1 and model membranes. Binding was seen to depend on both hydrophobic and electrostatic interactions, as well as lipid phase packing. Studies with water-soluble and membrane-bound fluorescence quenchers demonstrated that Trp3 is located close to the water,membrane interface. The results are discussed with regard to possible implications in receptor folding and function. © 2002 Wiley Periodicals, Inc. Biopolymers 65: 21,31, 2002 [source] | ||||||||||