Purification and properties of a (1→6)-β-glucanase from Acremonium sp. IMI 383068

Abstract

Several isolates of Acremonium sp. grew well on pustulan, a (1→6)-β-glucan, as sole carbon source and produced extracellular pustulan degrading enzymic activity. The extracellular enzymic activity of Acremonium sp. IMI 383068 against pustulan was due to the synthesis of a single (1→6)-β-glucanase, which was purified to homogeneity by FPLC. The molecular weight of this enzyme was estimated by SDS-PAGE to be 41.2 kDa. The enzyme is non-glycosylated with a pI of 4.5. It hydrolysed pustulan and lutean, both (1→6)-β-glucans, with a lower activity against lutean, and Eisenia bicyclis laminarin, a (1→3)(1→6)-β-glucan. Other substrates examined gave little or no detectable activity. TLC analyses of degradation products from enzymic digests of pustulan were consistent with the (1→6)-β-glucanase having an endo-hydrolytic mode of attack and it may be classified as glucan (1→6)-β-D-glucan glucanohydrolase [EC 3.2.1.75]. N-terminal sequence [SWIS-PROT P82288] analysis and BLAST searching revealed only a low level (ca 50%) of amino acid homology with the (1→6)-β-glucanase from Trichoderma harzianum, the only other fungal (1→6)-β-glucanase sequence contained in the data base. Furthermore, this homology was only revealed after alignment of the Acremonium sp. IMI 383068 sequence starting at amino acid 45 of the T. harzianum sequence, suggesting that the first 44 amino acids were missing from the Acremonium (1→6)-β-glucanase. The possible reasons for this are discussed. Homology was also seen with N-terminal amino acid sequences of several fungal (1→3)-β-glucanases.