Extracellular Soluble Polysaccharide (ESP) from Aspergillus kawachii Improves the Stability of Extracellular β-Glucosidases (EX-1 and EX-2) and Is Involved in Their Localization

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Aspergillus kawachii produces two extracellular β-glucosidases (EX-1 and EX-2) and one cell-wall-bound β-glucosidase (CB-1), all of which are derived from the same bglA gene. Extracellular β-glucosidases (EX-1 and EX-2) are stable in the crude solution form, but become unstable in the purified form under moderate conditions (pH 5.0 and 37℃). Purified extracellular β-glucosidases can bind to a mycelial cell wall fraction, even though these enzymes are released into the medium under solid culture conditions. A kawachii produces an extracellular soluble polysaccharide (ESP) under solid culture conditions. The addition of purified ESP markedly stabilized the β-glucosidases over the pH range of 3.0-7.0 and at temperatures below 50℃. ESP directly interacted with the purified extracellular β-glucosidases but did not affect the K_m values of these enzymes. Moreover, ESP inhibited the adsorption of purified extracellular β-glucosidases to the cell wall fraction and extracted them from it. These results indicate that ESP plays important roles in the stability and localization of extracellular β-glucosidases. ESP from A.kawachii directly binds to the enzymes and releases them to the medium from the cell wall layer and then stabilizes them.
社団法人日本生物工学会の論文
2001-02-25