Strengthening Of Hydrophobic Interactions Research Articles

Engineering non-conserved salt bridges in GH11 xylanase from Bacillus pumilus SSP34 for improved thermal stability: an in-silico evaluation

GH11 xylanases are commercially important enzymes for degradation of xylan fibers. We have identified the presence of nine non-conserved and five conserved salt bridges in GH11 xylanase from Bacillus pumilus SSP34. We have designed two sets of mutants viz., (1) substitution mutants in which non-conserved charged amino acid residues have been replaced with appropriate hydrophobic residues based on side chain occupancy and hydrophobicity and (2) deletion mutants where non-conserved charged residues have been deleted. The stability of the mutants has been evaluated in-silico by analyzing the contributions of non-covalent interactions like hydrophobic interaction clusters and salt bridges. The stability of the resultant mutants was evaluated using parameters such as radius of gyration, solvent accessible surface area, root mean square deviation, root mean square fluctuations and protein unfolding measurements using molecular dynamic simulations. The deletion of certain charged residues resulted in mutants having lowered radius of gyration and decreased surface areas. However, RMSD and RMSF measurements indicated lowered stability in comparison to substitution mutants. Of the substitution mutants, the SBM 3 was the most stable mutant as indicated by Rg, SASA, RMSF and simulated protein unfolding measurements. The major contributing factors for improved stability could be strengthening of hydrophobic interactions in the GH11 xylanase from B. pumilus. These in-silico stability measurements of salt bridge mutants may lead to better design of GH11 xylanases for commercial applications. Communicated by Ramaswamy H. Sarma

Interaction Mechanism of Anabolic Steroid Hormones with Structural Components of Erythrocyte Membranes

The interaction of testosterone, androsterone, dehydroepiandrosterone (DHEA), and dehydroepiandrosterone sulfate (DHEAS) with erythrocyte membranes was studied. It was shown that testosterone and androsterone have a high constant of binding to the membranes (K(b) ≈ 10(6) M(-1)), whereas K(b)'s for DHEA and DHEAS are 2 orders of magnitude lower. Hydrogen bonds and hydrophobic interactions play an important role in binding of anabolic steroids. Hydrogen bonds form with CO and NH groups both of membrane proteins and phospholipids. This results in the formation of complex domains rising above the surface of membranes. Strengthening of hydrophobic interactions in the domains promotes the displacement of water dipoles to adjacent regions, thus loosening the phospholipid bilayer. Overall, microviscosity of erythrocyte membranes strongly increases, which decreases the plasticity of erythrocytes and hampers their motion in blood capillaries. This mechanism may underlie the development of diffusion myocardial hypoxia and hypoxic cardiac arrest.

Stabilisation of ovalbumin by maltose

Sugars stabilise proteins against extremes of pH and heat denaturation. This was studied by means of density, ultrasonic velocity and viscosity measurements of the following systems (i) ovalbumin–phosphate buffer (pH 2.4, 5.2, 7.0 and 8.9) and (ii) ovalbumin–maltose–phosphate buffer (pH 2.4, 5.2, 7.0 and 8.9) systems as functions of concentration and temperature. The partial specific volumes ( ν ̄ 0 ), partial specific adiabatic compressibility ( β ̄ s ), intrinsic viscosity, [ η] and shape factor, ν, were calculated for the said systems. The results obtained from such studies suggest that the stabilisation of ovalbumin occurs in the presence of maltose through strengthening of hydrophobic interactions.

Structural changes and interactions involved in the Ca(2+)-triggered stabilization of the cell-bound cell envelope proteinase in Lactococcus lactis subsp. cremoris SK11.

The cell-bound cell envelope proteinase (CEP) of the mesophilic cheese-starter organism Lactococcus lactis subsp. cremoris SK11 is protected from rapid thermal inactivation at 25 degrees C by calcium bound to weak binding sites. The interactions with calcium are believed to trigger reversible structural rearrangements which are coupled with changes in specific activity (F. A. Exterkate and A. C. Alting, Appl. Env. Microbiol. 65:1390-1396, 1999). In order to determine the significance of the rearrangements for CEP stability and the nature of the interactions involved, the effects of the net charge present on the enzyme and of different neutral salts were studied with the stable Ca-loaded CEP, the unstable so-called "Ca-free" CEP and with the Ca-free CEP which was stabilized nonspecifically and essentially in its native conformation by the nonionic additive sucrose. The results suggest that strengthening of hydrophobic interactions is conducive to stabilization of the Ca-free CEP. On the other hand, a hydrophobic effect contributes significantly to the stability of the Ca-loaded CEP; a phased salting-in effect by a chaotropic salt suggests a complex inactivation process of this enzyme due to weakening of hydrophobic interactions and involving an intermediate enzyme species. Moreover, a Ca-triggered increase of a relatively significant hydrophobic effect in the sucrose-stabilized Ca-free CEP occurs. It is suggested that in the Ca-free CEP the absence of both local calcium-mediated backbone rigidification and neutralization of negative electrostatic potentials in the weak Ca-binding sites, and in addition the lack of significant hydrophobic stabilization, increase the relative effectiveness of electrostatic repulsive forces on the protein to an extent that causes the observed instability. The conditions in cheese seem to confer stability upon the cell-bound enzyme; its possible involvement in proteolysis throughout the ripening period is discussed.

General anesthetic agents and the conformation of proteins. 4. Strengthening of hydrophobic interaction in bovine and human serum albumins, in human transferrin, and in lysozyme by 1-alkanols and the cutoff effect in anesthetic potency

General anesthetic agents and the conformation of proteins. 4. Strengthening of hydrophobic interaction in bovine and human serum albumins, in human transferrin, and in lysozyme by 1-alkanols and the cutoff effect in anesthetic potency

General anesthetic agents and the conformation of proteins. 2. Strengthening of hydrophobic interaction in .beta.-lactoglobulin by 1-alkanols and the "cutoff" effect in anesthetic potency

Les effets de differents alcanols sur le pouvoir optique rotatoire de la β-lactoglobuline ont ete determines. Il apparait que le pouvoir anesthesiant des alcanols est lie a la capacite de renforcer l'interaction hydrophobe des proteines. La capacite de renforcer l'interaction hydrophobe depend de la concentration en proteine et de la longueur de la chaine de l'alcool. L'etude de l'influence de la longueur de la chaine permet de distinguer 2 regions (C 2 −C 12 et C 13 −C 16 )