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

Lysobacter enzymogenes strain N4-7 produces multiple biochemically distinct extracellular beta-1,3-glucanase activities. The gluA, gluB, and gluC genes, encoding enzymes with beta-1,3-glucanase activity, were identified by a reverse-genetics approach following internal amino acid sequence determination of beta-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 beta-1,3-glucanase activity. Biochemical analyses of the recombinant enzymes indicate that GluA and GluC exhibit maximal activity at pH 4.5 and 45 degrees C and that GluB is most active between pH 4.5 and 5.0 at 41 degrees C. Activity of recombinant proteins against various beta-1,3 glucan substrates indicates that GluA and GluC are most active against linear beta-1,3 glucans, while GluB is most active against the insoluble beta-1,3 glucan substrate zymosan A. These data suggest that the contribution of beta-1,3-glucanases to the biocontrol activity of L. enzymogenes may be due to complementary activities of these enzymes in the hydrolysis of beta-1,3 glucans from fungal cell walls.