pH dependent conformational and structural changes of xylanase from an alkalophilic thermophilic Bacillus sp (NCIM 59)

Biosynthesis of selenium nanoparticles using Klebsiella pneumoniae and their recovery by a simple sterilization process

The use of biologically derived metal nanoparticles for various proposes is going to be an issue of considerable importance; thus, appropriate methods should be developed and tested for the biological synthesis and recovery of these nanoparticles from bacterial cells. In this research study, a strain of Klebsiella pneumoniae was tested for its ability to synthesize elemental selenium nanoparticles from selenium chloride. A broth of Klebsiella pneumoniae culture containing selenium nanoparticles was subjected to sterilization at 121(o)C and 17 psi for 20 minutes. Released selenium nanoparticles ranged in size from 100 to 550 nm, with an average size of 245 nm. Our study also showed that no chemical changes occurred in selenium nanoparticles during the wet heat sterilization process. Therefore, the wet heat sterilization process can be used successfully to recover elemental selenium from bacterial cells.

One-step purification and characterization of cellulase-free xylanase produced by alkalophilic Bacillus subtilis ash

The present study describes the one-step purification and characterization of an extracellular cellulase-free xylanase from a newly isolated alkalophilic and moderately thermophilic strain of Bacillus subtilis ASH. Xylanase was purified to homogeneity by 10.5-fold with ~43% recovery using ion-exchange chromatography through CM-Sephadex C-50. The purified enzyme revealed a single band on SDS-PAGE gel with a molecular mass of 23 kDa. It showed an optimum pH at 7.0 and was stable over the pH range 6.0-9.0. The optimum temperature for enzyme activity was 55 °C. The purified xylanase did not lose any activity up to 45 ºC, however, it retained 80% and 51% of its activity after pre-incubation at 55 ºC and 60 ºC, respectively. The enzyme obeyed Michaelis-Menton kinetics towards birch wood xylan with apparent K_m 3.33 mg/ml and V_max 100 IU/ml. The enzyme was strongly inhibited by Hg²⁺and Cu²⁺while enhanced by Co²⁺ and Mn²⁺. The purified enzyme could be stored at 4 ºC for six weeks without any loss of catalytic activity. The faster and economical purification of the cellulase-free xylanase from B. subtilis ASH by one-step procedure together with its appreciable stability at high temperature and alkaline pH makes it potentially effective for industrial applications.

Glycine-assisted enhancement of 1,4-β-d-xylan xylanohydrolase activity at alkaline pH with a pH optimum shift

This is the first report describing the enhancement of xylanase activity by the neutral amino acid glycine. Xylanase activity is increased seven-fold at alkaline pH in the presence of glycine and its pH optimum is shifted from pH 7 to 8 without using any protein engineering techniques. Analysis of the steady-state kinetics revealed that glycine in the reaction mixture increases the K m and k cat values of the enzyme. Chemoaffinity labeling and studies using glycine esters indicate an involvement of the carboxylate ion of glycine in enhancing xylanase catalytic activity. A novel possible mechanism for the glycine-assisted catalytic action of xylanase is proposed.

Acid-induced partly folded conformation resembling a molten globule state of xylanase from an alkalothermophilic Bacillus sp

Nonnative protein structures having a compact secondary, but not rigid tertiary structure, have been increasingly observed as intermediate states in protein folding. We have shown for the first time during acid-induced unfolding of xylanase (Xyl II) the presence of a partially structured intermediate form resembling a molten globule state. The conformation and stability of Xyl II at acidic pH was investigated by equilibrium unfolding methods. Using intrinsic fluorescence and CD spectroscopic studies, we have established that Xyl II at pH 1.8 (A-state) retains the helical secondary structure of the native protein at pH 7.0, while the tertiary interactions are much weaker. At variance, from the native species (N-state), Xyl II in the A-state binds 1-anilino-8-sulfonic acid (ANS) indicating a considerable exposure of aromatic side chains. Lower concentration of Gdn HCl are required to unfold the A-state. For denaturation by Gdn HCl, the midpoint of the cooperative unfolding transition measured by fluorescence for the N-state is 3.5 +/- 0.1 M, which is higher than the value (2.2 +/- 0.1 M) observed for the A-state at pH 1.8. This alternatively folded state exhibits certain characteristics of the molten globule but differs distinctly from it by its structural stability that is characteristic for native proteins.