Molecular cloning, purification and characterization of thermostable <img src='/image/spc_char/beta.gif' border=0>-1,3-1,4 glucanase from <i>Bacillus subtilis </i>A8-8

Abstract

A gene encoding a <img src='/image/spc_char/beta.gif' border=0>-1,3-1,4-glucanase (<i style="">Cel</i>A) belonging to family 5 of glycoside hydrolases was cloned and sequenced from the <i>Bacillus subtilis</i> A8-8. The open-reading-frame of <i style="">celA </i>comprised 1499 base pairs and the enzyme was composed of 500 amino acids with a molecular mass of 55 kDa. The recombinant <img src='/image/spc_char/beta.gif' border=0>-1,3-1,4 glucanase was purified by GST-fusion purification system. The pH and temperature optima of the enzyme were 8.0 and 60^oC, respectively. The enzyme was stable within pH 6.0-9.0. It was stable up to 60^oC and retained 30% of its original activity at 70^oC for 60 min. It hydrolyzed lichenan, CMC, xylan, laminarin, avicel and <i style="">p</i>NPC, but was inactive towards cellobiose. The enzyme activity was markedly activated by Co²⁺ and Mn²⁺, but was strongly inactivated by Fe³⁺. The truncated gene, devoid of cellulose-binding domain (CBD) showed 60% of activity and bound to avicel.