Activation of NADPH-dependent superoxide production in a cell-free system by sodium dodecyl sulfate

Sodium dodecyl sulfate (SDS) elicits the production of superoxide (O2-) by a cell-free system represented by sonically disrupted guinea pig peritoneal macrophages. O2- generation requires NADPH and a heat-sensitive cellular component, is proportional to the amount of macrophage protein, and exhibits a pH optimum of 6.5-7. The kinetic parameters of the SDS-stimulated enzyme are: Km (+/- S.E.) = 0.0367 +/- 0.003 mM NADPH and Vmax (+/- S.E.) = 73.46 +/- 9.09 nmol O2-/mg of protein/min. O2- production is dependent on the cooperation between a particulate subcellular component sedimentable at 48,000 X g and a cytosolic factor present in the 48,000 X g supernatant. The activity of both components is destroyed by heating at 80 degrees C. Pretreatment of intact macrophages with phorbol myristate acetate results in the partial removal of the requirement for cytosolic factor; SDS is now capable of activating the isolated 48,000 X g pellet. Among a large number of anionic, cationic, and nonionic detergents tested, only the anionic detergents SDS and sodium dodecyl sulfonate are capable of eliciting O2- production in the cell-free system, SDS being the more potent stimulant. It is proposed that the structural requirements that make these compounds capable of activating the O2- forming NADPH oxidase in a cell-free system are the presence of an anionic polar head and a long hydrophobic alkyl tail. We suggest that sodium salts of long chain unsaturated fatty acids that were found by us to be capable of stimulating O2- production in a cell-free system (Bromberg, Y., and Pick, E. (1984) Cell. Immunol. 88, 213-221) owe their activity to the fact that they function as anionic detergents.     

Inactivation of prions by acidic sodium dodecyl sulfate

Prompted by the discovery that prions become protease-sensitive after exposure to branched polyamine dendrimers in acetic acid (AcOH) (S. Supattapone, H. Wille, L. Uyechi, J. Safar, P. Tremblay, F. C. Szoka, F. E. Cohen, S. B. Prusiner, and M. R. Scott, J. Virol. 75:3453-3461, 2001), we investigated the inactivation of prions by sodium dodecyl sulfate (SDS) in weak acid. As judged by sensitivity to proteolytic digestion, the disease-causing prion protein (PrPSc) was denatured at room temperature by SDS at pH values of < or =4.5 or > or =10. Exposure of Sc237 prions in Syrian hamster brain homogenates to 1% SDS and 0.5% AcOH at room temperature resulted in a reduction of prion titer by a factor of ca. 10(7); however, all of the bioassay hamsters eventually developed prion disease. When various concentrations of SDS and AcOH were tested, the duration and temperature of exposure acted synergistically to inactivate both hamster Sc237 prions and human sporadic Creutzfeldt-Jakob disease (sCJD) prions. The inactivation of prions in brain homogenates and those bound to stainless steel wires was evaluated by using bioassays in transgenic mice. sCJD prions were more than 100,000 times more resistant to inactivation than Sc237 prions, demonstrating that inactivation procedures validated on rodent prions cannot be extrapolated to inactivation of human prions. Some procedures that significantly reduced prion titers in brain homogenates had a limited effect on prions bound to the surface of stainless steel wires. Using acidic SDS combined with autoclaving for 15 min, human sCJD prions bound to stainless steel wires were eliminated. Our findings form the basis for a noncorrosive system that is suitable for inactivating prions on surgical instruments, as well as on other medical and dental equipment.     

Denaturation of MM-creatine kinase by sodium dodecyl sulfate

The denaturation of dimeric cytoplasmic MM-creatine kinase by sodium dodecyl sulfate (SDS) has been investigated using activity measurements, far-ultraviolet circular dichroism, SEC-HPLC, electric birefringence, intrinsic probes (cysteine and tryptophan residues), and an extrinsic fluorescent probe (ANS). Our results show that inactivation is the first detectable event; the inactivation curve midpoint is located around 0.9 mM SDS. The second event is dissociation and it occurs in parallel to tertiary and secondary perturbations, as demonstrated by the coincidence (near 1.3 mM) of the midpoints of the transition curves monitoring dissociation and structural changes. At high total SDS concentration (concentration higher than 2.5 mM), the monomer had bound 170 mol of SDS per mol of protein. In these conditions, electric birefringence experiments suggest that the SDS-CK complex may be described as a prolate ellipsoid with an axial ratio of 1.27 (14 nm×11 nm). These results are compatible with recent models of SDS-protein complexes: the protein decorated micelle structure or the necklace structure.     

Enhanced lipoxygenase activity is involved in barley root tip swelling induced by cadmium,auxin or hydrogen peroxide

Lipoxygenases (EC 1.13.11.12) catalyse the formation of hydroperoxy derivates by oxygenation of polyunsaturated fatty acids. They act as signal molecules, triggering several developmental processes and defence responses under stress conditions. Incubation of Cd-, IAA- or H₂O₂-short-term treated seedlings in the presence of LOX inhibitors efficiently inhibited both Cd-, IAA- or H₂O₂-induced LOX activity and root swelling in a concentration dependent manner, suggesting a key role of LOX or LOX signalling pathway in radial expansion of root cells. Application of antioxidants (ascorbate or N-acetyl cysteine) to the treated seedlings at low 2 mM concentration did not affect the Cd-, IAA- or H₂O₂-induced LOX activity and root swelling. At higher, 10 mM concentration antioxidants markedly inhibited root growth, significantly increased the activity of LOX and evoked the radial expansion of root cells leading to root swelling with well developed root hairs already in control roots. By contrast, the lipophilic antioxidant trolox, a scavenger of hydroperoxides, severely inhibited the development of Cd-, IAA- or H₂O₂-induced root swelling, indicating that not directly LOX, but probably oxylipins, products of LOX pathway, are involved in the induction of root swelling in barley root tip. The results of this study suggest a strong connection between abiotic stress-induced alteration in redox and hormone status caused root growth inhibition and LOX pathway mediated radial expansion of root tip cells.     

Overlapping between fluorescence modifications and activation of prostate transglutaminase induced by sodium dodecyl sulfate.

The transglutaminase from rat coagulating gland secretion has been proposed as a new member of the transglutaminase family. Its basal activity is about 11-fold lower than those of other transglutaminases (e.g., the cytosolic tissue transglutaminase), but reaches levels comparable to those of other transglutaminases on addition of specific surfactant agents. There is no study devoted to understanding the molecular basis of this apparently anomalous activation, which is maximal at approximately 1.5 mM sodium dodecyl sulfate. We provide evidence that in the presence of this detergent modifications of the intrinsic fluorescence as well as energy transfer of the protein fluorescence to a micellar probe parallel the activation of the enzyme. As the sodium dodecyl sulfate concentration inducing maximal activation equals the critical micellar concentration, the biological activity of this transglutaminase appears to be modulated by the binding of micellar aggregates. In fact, the enzyme is modified by posttranslational modifications consisting of some lipid tails. At least two of these tails could act as aggregation nuclei of the enzyme with detergents. This behavior is different from that typical of molecular forms purified from other sources.     

Secondary structure transitions and aggregation induced in dynorphin neuropeptides by the detergent sodium dodecyl sulfate

Dynorphins, endogeneous opioid neuropeptides, function as ligands to the opioid kappa receptors and also induce non-opioid effects in neurons, probably related to direct membrane interactions. We have characterized the structure transitions of dynorphins (big dynorphin, dynorphin A and dynorphin B) induced by the detergent sodium dodecyl sulfate (SDS). In SDS titrations monitored by circular dichroism, we observed secondary structure conversions of the peptides from random coil to α-helix with a highly aggregated intermediate. As determined by Fourier transform infrared spectroscopy, this intermediate exhibited β-sheet structure for dynorphin B and big dynorphin. In contrast, aggregated dynorphin A was α-helical without considerable β-sheet content. Hydrophobicity analysis indicates that the YGGFLRR motif present in all dynorphins is prone to be inserted in the membrane. Comparing big dynorphin with dynorphin A and dynorphin B, we suggest that the potent neurotoxicity of big dynorphin could be related to the combination of amino acid sequences and secondary structure propensities of dynorphin A and dynorphin B, which may generate a synergistic effect for big dynorphin membrane perturbing properties. The induced aggregated α-helix of dynorphin A is also correlated with membrane perturbations, whereas the β-sheet of dynorphin B does not correlate with membrane perturbations.     

Effect of calcium on sulfate uptake by barley roots

Abstract Sulfate uptake by excised roots of barley (Hordeum vulgare L.) was maximal in the presence of about 3x10^-3M CaCl₂. Kinetic studies contraindicate a stoichiometric binding of calcium to the carrier for sulfate, in contrast to findings of Cuppoletti and Segel (Biochemistry 14: 471–4718, 1975) for the filamentous fungus Penicillium notatum. In barley, calcium affects the K_m but not the V_max for sulfate uptake, presumably by altering the conformation and, thereby, the affinity of the carrier. Calcium also affects the transition site for sulfate uptake.     

Isoelectric focusing of proteins exposed to sodium dodecyl sulfate

We have found that proteins that have been dissolved in sodium dodecyl sulfate, an anionic detergent, can be successfully analyzed by isoelectric focusing. Optimal results are obtained if the protein in SDS solution is dialyzed against a large excess of 10 m urea, to remove as much SDS as possible, prior to focusing.     

Structural changes of a sodium dodecyl sulfate (SDS) micelle induced by alcohol molecules

Coarse-grained dynamical simulations have been performed to investigate the behavior of a surfactant micelle in the presence of six different alcohols: hexanol, octanol, decanol, dodecanol, tetradecanol, and hexadecanol. The self-assembly of sodium dodecyl sulfate (SDS) is modified by the alcohol molecules into cylindrical and bilayer micelles as a function of the alcohol/SDS mass ratio. Therefore, in order to understand, from a molecular point of view, how SDS and alcohol molecules self-organize to form the new micelles, different studies were carried out. Analysis of micelle structures, density profiles, and parameters of order were conducted to characterize the shape and size of those micelles. The density profiles revealed that the alcohol molecules were located at the water–micelle interface next to the SDS molecules at low alcohol/SDS mass ratio. At high alcohol/SDS mass ratios, alcohol molecules moved to the middle of the micelle by increasing their size and by producing a structural change. Moreover, micelle structures and sizes were influenced not only by the alcohol/SDS mass ratio but also by the order of the SDS and alcohol tails. Finally, the size of the micelles and enthalpy calculations were used as order parameters to determine a structural phase diagram of alcohol/SDS mixtures in water.

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Graphical Abstract Structural transition of SDS/alcohol mixtures

     

Activation of tobacco leaf polyphenol oxidase by sodium dodecyl sulfate

The effect of sodium dodecyl sulfate (SDS) on purified tobacco leaf PPO (PPO II) was investigated at various pHs and temperatures. SDS increased the activity of PPO II due to the formation of SDS-PPO II complex, leading to conformational changes, thus making access to active center easier. The relationship between the activity and the molar ratio of SDS-PPO II to PPO II showed that the critical point reached a plateau of activity at the molar ratio of about 1.2. The pH had a significant effect on interaction between SDS and PPO II, as compared to PPO II. The optimum catalytic temperature of the complex rose by 10 degrees C, suggesting that stabilization of the structure had been improved by the formation of complex.     

Involvement of electrostatic interactions in the mechanism of peptide folding induced by sodium dodecyl sulfate binding

Sodium dodecyl sulfate (SDS) has consistently been shown to induce secondary structure, particularly alpha-helices, in polypeptides, and is commonly used to model membrane and other hydrophobic environments. However, the precise mechanism by which SDS induces these conformational changes remains unclear. To examine the role of electrostatic interactions in this mechanism, we have designed two hydrophilic, charged amphipathic alpha-helical peptides, one basic (QAPAYKKAAKKLAES) and the other acidic (QAPAYEEAAEELAKS), and their structures were studied by CD and NMR. The design of the peptides is based on the sequence of the segment of residues 56-70 of human platelet factor 4 [PF4(56-70), QAPLYKKIIKKLLES]. Both peptides were unstructured in water, and in the presence of neutral, zwitterionic, or cationic detergents. However, in SDS at neutral pH, the basic peptide folded into an alpha-helix. By contrast, the pH needed to be lowered to 1.8 before alpha-helix formation was observed for the acidic peptide. Strong, attractive electrostatic interactions, between the anionic groups of SDS and the cationic groups of the lysines, appeared to be necessary to initiate the folding of the basic peptide. NMR analysis showed that the basic peptide was fully embedded in SDS-peptide micelles, and that its three-dimensional alpha-helical structure could be superimposed on that of the native structure of PF4(56-70). These results enabled us to propose a working model of the basic peptide-SDS complex, and a mechanism for SDS-induced alpha-helical folding. This study demonstrates that, while the folding of peptides is mostly driven by hydrophobic effects, electrostatic interactions play a significant role in the formation and the stabilization of SDS-induced structure.     

Changes in tyrosinase specificity by ionic liquids and sodium dodecyl sulfate

Tyrosinase is a member of the type 3 copper enzyme family involved in the production of melanin in a wide range of organisms. The ability of tyrosinases to convert monophenols into diphenols has stimulated studies regarding the production of substituted catechols, important intermediates for the synthesis of pharmaceuticals, agrochemicals, polymerization inhibitors, and antioxidants. Despite its enormous potential, the use of tyrosinases for catechol synthesis has been limited due to the low monophenolase/diphenolase activity ratio. In the presence of two water miscible ionic liquids, [BMIM][BF₄] and ethylammonium nitrate, the selectivity of a tyrosinase from Bacillus megaterium (TyrBm) was altered, and the ratio of monophenolase/diphenolase activity increased by up to 5-fold. Furthermore, the addition of sodium dodecyl sulphate (SDS) at levels of 2–50 mM increased the activity of TyrBm by 2-fold towards the natural substrates l-tyrosine and l-Dopa and 15- to 20-fold towards the non-native phenol and catechol. The R209H tyrosinase variant we previously identified as having a preferential ratio of monophenolase/diphenolase activity was shown to have a 45-fold increase in activity towards phenol in the presence of SDS. We propose that the effect of SDS on the ability of tyrosinase to convert non-natural substrates is due to the interaction of surfactant molecules with residues located at the entrance to the active site, as visualized by the newly determined crystal structure of TyrBm in the presence of SDS. The effect of SDS on R209 may enable less polar substrates such as phenol and catechol, to penetrate more efficiently into the enzyme catalytic pocket.     

Oxidative damages induced by short-term exposure to cadmium in bean plants: Protective role of salicylic acid

The role of salicylic acid (SA) in alleviating cadmium (Cd) toxicity was investigated in a hydroponic cultivation system. Short-term exposure of bean (Phaseolus vulgaris) plants to 20 μM Cd inhibited biomass production and intensively increased accumulation of Cd in both roots and leaves. At leaf level, Cd significantly decreased mineral ions, chlorophyll and carotenoids concentrations. Concomitantly, Cd enhanced electrolyte leakage, H₂O₂ content and lipid peroxidation as indicated by malondialdehyde (MDA) accumulation. SA pretreatment decreased the uptake and the transport of Cd, alleviated the Cd-induced inhibition of nutrient absorption and led to a significant increase of chlorophyll and carotenoid content. SA application alleviated the oxidative damages as evidenced by the lowered H₂O₂ and MDA content. SA particularly induced an increase in both CAT and APX activities accompanied by a significant reduction in SOD and POD activities. As important antioxidants, ascorbate and glutathione contents in bean leaves exposed to cadmium were significantly decreased by SA treatment. These results reveal the potentiating effect of salicylic acid in regulating cadmium induced oxidative stress in bean plants.     

Prestaining of glycoproteins in sodium dodecyl sulfate polyacrylamide gels by dansylhydrazine

A new fluorescent prestaining method for gel‐separated glycoproteins in 1D and 2D SDS‐PAGE was developed by using dansylhydrazine in this study. The prestained gels could be easily imaged after electrophoresis without any time‐consuming steps needed for poststains. As low as 4–8 ng glycoproteins (transferrin, α1‐acid glycoprotein) could be selectively detected, which is comparable to that of Pro‐Q Emerald 488, one of the most commonly used glycoprotein stain. In addition, a subsequent study of deglycosylation, glycoprotein affinity isolation, and LC‐MS/MS analysis was performed to confirm the specificity of the newly developed method.