Homology Model of a Novel Thermostable Xylanase fromBacillus subtilis-AK1

Abstract

Xylanases are glycosyl hydrolases that catalyze the hydrolysis of internal beta-1,4 glycosidic bonds of xylan, the major hemi-cellulose component of the plant cell wall. Enzymes such as xylanases are used considerably in industries. Their industrial usage is especially attractive since they can replace some of the environmental pollutants. We have earlier isolated a family 11-xylanase gene from Bacillus subtilis-AK1, which is active at high temperature as well as at alkaline pH. In order to understand the factors liable for the adaptation of this enzyme, three dimensional model of B. subtilis-AK1 xylanase has now been obtained by homology modeling. Modeling was carried out using Molecular Operating Environment (MOE) software developed by Chemical Computing Group Inc., running on Pentium IV workstation. The model showed that B. subtilis-AK1 xylanase having molecular weight around 20 kDa contains in its fold an alpha-helix and two beta-sheets packed against each other forming a beta-sandwich. The conserved active site amino acids E78R, Y80L were mutated in this novel B. subtilis-AK1 strain, but the protein folding and the function was maintained with high thermal stability. Several minor modifications appeared to be responsible for the increased thermo stability of AK1. Docking studies of the substrate xylan with -AK1 shows the possibility of the Arg 78 acting as the nucleophile instead of Glu 78.

Application of neural networks methods to define the most important features contributing to xylanase enzyme thermostability

“…Pre-treating paper pulp with xylanases can enhance the efficiency of the chemical extraction of lignin and so reduce the amounts of chlorine and chlorine dioxide required [30,31]. However, such applications require xylanase(s) with particular properties, the bio-bleaching of paper pulp requires a xylanase with better thermostability [32]. Two approaches have been taken: screening organisms from various sources in nature for high xylanase activity, and engineering known xylanases to improve their characteristics.…”