Molecular characterization and expression in Escherichia coli of three β-1,3-glucanase genes from Lysobacter enzymogenes strain N4-7

Lysobacter enzymogenes strain N4-7 produces multiple biochemically distinct extracellular β-1,3-glucanase activities. The gluA, gluB, and gluC genes, encoding enzymes with β-1,3-glucanase activity, were identified by a reverse-genetics approach following internal amino acid sequence determination of β-1,3-glucanase-active proteins partially purified from culture filtrates of strain N4-7. Analysis of gluA and gluC gene products indicates that they are members of family 16 glycoside hydrolases that have significant sequence identity to each other throughout the catalytic domain but that differ structurally by the presence of a family 6 carbohydrate-binding domain within the gluC product. Analysis of the gluB gene product indicates that it is a member of family 64 glycoside hydrolases. Expression of each gene in Escherichia coli resulted in the production of proteins with β-1,3-glucanase activity. Biochemical analyses of the recombinant enzymes indicate that GluA and GluC exhibit maximal activity at pH 4.5 and 45°C and that GluB is most active between pH 4.5 and 5.0 at 41°C. Activity of recombinant proteins against various β-1,3 glucan substrates indicates that GluA and GluC are most active against linear β-1,3 glucans, while GluB is most active against the insoluble β-1,3 glucan substrate zymosan A. These data suggest that the contribution of β-1,3-glucanases to the biocontrol activity of L. enzymogenes may be due to complementary activities of these enzymes in the hydrolysis of β-1,3 glucans from fungal cell walls.