Purification and characterization of the extracellular β-1,6-glucanases from the fungus Acremonium strain OXF C13 and isolation of the gene/s encoding these enzymes

Two extracellular β-1,6-glucanases were isolated, purified and characterized from culture filtrates of the fungus Acremonium OXF C13 grown with pustulan as sole carbon source. Both behaved as endo-acting enzymes and shared other biochemical characteristics, but differed in their molecular weights. The N-terminal amino acid sequence data from one of these, BGN6.1, showed high similarity to all other fungal β-1,6-glucanases so far sequenced. These sequence data were used to design PCR primers to isolate the gene encoding BGN6.1 from a genomic DNA library. This gene contained a putative 77 bp intron within an open reading frame of 1296 bp encoding 432 amino acids. A putative TATA motif was present at −84, and a potential creA consensus sequence of SYGGRG was seen at position −111. Comparing the experimentally determined N-terminal sequence data with the deduced amino acid sequence from the BGN6.1 gene indicates that the mature protein starts at amino acid 41 and Lys-Arg (KR), a known KEX2 protease recognition site immediately precedes the N-terminal amino acids. A further predicted signal cleavage site for the prepeptide was seen between amino acids 17 and 18. Similarities between this gene and those encoding other fungal β-1,6-glucanases are discussed. As no N-terminal amino acid sequence data could be obtained for the second β-1,6-glucanase from Acremonium OXF C13, internal peptides were sequenced instead. However, none of these sequences showed homology to the BGN6.1 glucanase, suggesting that the BGN6.1 and BGN6.2 glucanases are encoded by different genes.