A comparative study of the unfolding of the endoglucanase Cel45 from Humicola insolens in denaturant and surfactant. (1/199)

Cellulases are increasingly being used for industrial purposes, particularly in washing powders, yet little is known of the factors governing the stability of proteins in detergent solutions. We present a comparative analysis of the behavior of the cellulase Cel45 from Humicola insolens in the presence of the denaturant guanidinium chloride and the anionic detergent C12-LAS. Although Cel45 unfolds in GdmCl according to a simple two-state model under equilibrium conditions, it accumulates a transient intermediate during refolding. The four disulfide bonds do not contribute detectably to the stability of the native state. Cel45 is unfolded by very low concentrations of C12-LAS (1-4 mM). An analysis of 16 mutants of Cel45 shows a very weak correlation between unfolding rates in denaturant and detergent; mutants that have the same unfolding rate in GdmCl (within a factor of 1.5) vary 1,000-fold in their unfolding rates in C12-LAS. The data support a simple model for unfolding by detergent, in which the introduction of positive charges or removal of negative charges greatly increases detergent sensitivity, while interactions with the hydrophobic detergent tail contribute to a smaller extent. This implies that different detergent-mediated unfolding pathways exist, whose accessibilities depend on individual residues. Double-mutant cycles reveal that mutations in two proximal residues lead to repulsion and a destabilization greater than the sum of the individual mutations as measured by GdmCl denaturation, but they also reduce the affinity for LAS and therefore actually stabilize the protein relative to wild-type. Ligands that interact strongly with the denatured state may therefore alter the unfolding process.  (+info)

Effects of carnosine and related compounds on the stability and morphology of erythrocytes from alcoholics. (2/199)

The effects of carnosine and related compounds on erythrocytes from alcoholics were studied. In their presence, erythrocytes showed an increased ability to resist haemolysis and showed a more normal morphology, with carnosine and N-acetyl-carnosine being the most effective compounds. These beneficial properties of the dipeptides do not appear to be directly related to their antioxidant or buffering properties.  (+info)

Mechanism for proton conduction of the M(2) ion channel of influenza A virus. (3/199)

The M(2) integral membrane protein of influenza A virus forms a proton-selective ion channel. We investigated the mechanism for proton transport of the M(2) protein in Xenopus oocytes using a two-electrode voltage clamp and in CV-1 cells using the whole cell patch clamp technique. Membrane currents were recorded while manipulating the external solution to alter either the total or free proton concentration or the solvent itself. Membrane conductance decreased by approximately 50% when D(2)O replaced H(2)O as the solvent. From this, we conclude that hydrogen ions do not pass through M(2) as hydronium ions, but instead must interact with titratable groups that line the pore of the channel. M(2) currents measured in solutions of low buffer concentration (<15 mM in oocytes and <0.15 mM in CV-1 cells) were smaller than those studied in solutions of high buffer concentration. Furthermore, the reversal voltage measured in low buffer was shifted to a more negative voltage than in high buffer. Also, at a given pH, M(2) current amplitude in 15 mM buffer decreased when pH-pK(a) was increased by changing the buffer pK(a). Collectively, these results demonstrate that M(2) currents can be limited by external buffer capacity. The data presented in this study were also used to estimate the maximum single channel current of the M(2) ion channel, which was calculated to be on the order of 1-10 fA.  (+info)

In vivo transposon mutagenesis of the methanogenic archaeon Methanosarcina acetivorans C2A using a modified version of the insect mariner-family transposable element Himar1. (4/199)

We present here a method for in vivo transposon mutagenesis of a methanogenic archaeon, Methanosarcina acetivorans C2A, which because of its independence from host-specific factors may have broad application among many microorganisms. Because there are no known Methanosarcina transposons we modified the mariner transposable element Himar1, originally found in the insect Hematobia irritans, to allow its use in this organism. This element was chosen because, like other mariner elements, its transposition is independent of host factors, requiring only its cognate transposase. Modified mini-Himar1 elements were constructed that carry selectable markers that are functional in Methanosarcina species and that express the Himar1 transposase from known Methanosarcina promoters. These mini-mariner elements transpose at high frequency in M. acetivorans to random sites in the genome. The presence of an Escherichia coli selectable marker and plasmid origin of replication within the mini-mariner elements allows facile cloning of these transposon insertions to identify the mutated gene. In preliminary experiments, we have isolated numerous mini-mariner-induced M. acetivorans mutants, including ones with insertions that confer resistance to toxic analogs and in genes that encode proteins involved in heat shock, nitrogen fixation, and cell-wall structures.  (+info)

Crystallization and preliminary X-ray crystallographic analysis of NADPH: azodicarbonyl/quinone oxidoreductase, a plant zeta-crystallin. (5/199)

Arabidopsis thaliana P1 protein was crystallized using the hanging drop vapor-diffusion method in 0.1 M piperazine-1, 4-bis(2-ethanesulfonic acid) buffer, containing 14% polyethylene glycol 6000 and 0.2 M magnesium acetate at pH 6.5 and 20 degrees C. The crystals are orthorhombic and belong to the space group P2(1)2(1)2(1) with unit cell dimensions of a=49.8, b=122.4 and c=149. 9 A. The diffraction data up to 2.9 A were collected by a multiwire area detector.  (+info)

Conservation of phosphorylation state of cardiac phosphofructokinase during in vitro hypothermic hypoxia. (6/199)

We investigated the metabolic effects of buffering agents alpha-amino-4-imidazole-propionic acid (Histidine), N, N-bis(2-hydroxyethyl)glycine (bicine), N, N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES) on anaerobic energy production (via glycolysis) and conservation of key regulatory enzyme activity, and phosphofructokinase (PFK) throughout prolonged hypothermic hypoxia in porcine hearts. Hearts from 35 to 40 kg pigs were flushed with one of the following five solutions: St. Thomas' Hospital solution (STHS); modified University of Wisconsin (UW) solution; and three solutions containing modified UW plus 90 mM of histidine, bicine, or BES. The hearts were then stored at 4 degrees C for 10 h. After 10 h of hypothermic hypoxia, lactate values were 6.7-12.9 micromol/g higher than control; this reflected an increase in anaerobic end product of 35-67%. The consequences of enhanced anaerobic metabolism were higher ATP, total adenylate, Energy Charge, and ATP/ADP ratios in most of the buffered groups after 4-10 h cold storage; effectiveness of the buffers employed correlated with buffering capacity (BES proved to be the most effective). PFK remained activated throughout most of the 10-h period in hearts stored with buffers and did not undergo the rapid inactivation experienced by hearts stored in STHS. Conservation of PFK integrity with buffering agents was not related to a pH-mediated event; changes in kinetic parameters suggested that this protection was due to an irreversible posttranslational modification, specifically a dephosphorylation event.  (+info)

The origins of stability of spontaneous vesicles. (7/199)

Equilibrium unilamellar vesicles are stabilized by one of two distinct mechanisms depending on the value of the bending constant. Helfrich undulations ensure that the interbilayer potential is always repulsive when the bending constant, K, is of order k(B)T. When K k(B)T, unilamellar vesicles are stabilized by the spontaneous curvature that picks out a particular vesicle radius; other radii are disfavored energetically. We present measurements of the bilayer elastic constant and the spontaneous curvature, R(o), for three different systems of equilibrium vesicles by an analysis of the vesicle size distribution determined by cryo-transmission electron microscopy and small-angle neutron scattering. For cetyltrimethylammonium bromide (CTAB)/sodium octyl sulfonate catanionic vesicles, K =.7 k(B)T, suggesting that the unilamellar vesicles are stabilized by Helfrich-undulation repulsions. However, for CTAB and sodium perfluorooctanoate (FC(7)) vesicles, K = 6 k(B)T, suggesting stabilization by the energetic costs of deviations from the spontaneous curvature. Adding electrolyte to the sodium perfluorooctanoate/CTAB vesicles leads to vesicles with two bilayers; the attractive interactions between the bilayers can overcome the cost of small deviations from the spontaneous curvature to form two-layer vesicles, but larger deviations to form three and more layer vesicles are prohibited. Vesicles with a discrete numbers of bilayers at equilibrium are possible only for bilayers with a large bending modulus coupled with a spontaneous curvature.  (+info)

2-Bromoethanesulfonate affects bacteria in a trichloroethene-dechlorinating culture. (8/199)

Long-term exposure to 2-bromoethanesulfonate (BES), an agent known to inhibit methanogenesis, altered the bacterial community structure of an anaerobic enrichment culture that reductively dechlorinated trichloroethene (TCE). BES did not hinder the dechlorination of TCE or other chlorinated ethenes as previously reported, although different intermediates and end products were observed.  (+info)

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