ABSTRACTFour types of β-1,3-1,4 glucanase (β-glucanase, EC 3.2.1.73) genes, designatedbglA13,bglA16,bglA51, andbglM2, were found in the cDNA library ofNeocallimastix patriciarumJ11. All were highly homologous with each other and demonstrated a close phylogenetic relationship with and a similar codon bias toStreptococcus equinus. The presence of expansion and several predicted secondary structures in the 3′ untranslated regions (3′UTRs) ofbglA16andbglM2suggest that these two genes were duplicated recently, whereasbglA13andbglA16, which contain very short 3′UTRs, were replicated earlier. These findings indicate that the β-glucanase genes fromN. patriciarumJ11 may have arisen by horizontal transfer from the bacterium and subsequent duplication in the rumen fungus. β-Glucanase genes ofStreptococcus equinus,Ruminococcus albus7, andN. patriciarumJ11 were cloned and expressed byEscherichia coli. The recombinant β-glucanases cloned fromS. equinus,R. albus7, andN. patriciarumJ11 were endo-acting and had similar substrate specificity, but they demonstrated different properties in other tests. The specific activities and catalytic efficiency of the bacterial β-glucanases were also significantly lower than those of the fungal β-glucanases. Our results also revealed that the activities and some characteristics of enzymes were changed during the horizontal gene transfer event. The specific activities of the fungal β-glucanases ranged from 26,529 to 41,209 U/mg of protein when barley-derived β-glucan was used as the substrate. They also demonstrated similar pH and temperature optima, substrate specificity, substrate affinity, and hydrolysis patterns. Nevertheless, BglA16 and BglM2, two recently duplicated β-glucanases, showed much higherkcatvalues than others. These results support the notion that duplicated β-glucanase genes, namely,bglA16andbglM2, increase the reaction efficiency of β-glucanases and suggest that the catalytic efficiency of β-glucanase is likely to be a criterion determining the evolutionary fate of duplicate forms inN. patriciarumJ11.
A highly efficient β-glucosidase from the buffalo rumen fungus Neocallimastix patriciarum W5
