Abstract
An endo-polygalacturonase gene, pga1, was cloned from the acidophilic fungus Bispora sp. MEY-1 and expressed in Pichia pastoris. The 1455-bp full-length complementary DNA of pga1 encoded a 485-amino acid polypeptide (endo-PGA1) including a putative 21-residue signal peptide and a catalytic domain belonging to glycoside hydrolase family 28. Purified recombinant endo-PGA1 exhibited activity towards polygalacturonic acid and pectin was optimally active at pH 3.5 and 50 °C, and showed good stability at pH 2.0–7.0. When tested against pectin, endo-PGA1 exhibited 40% of maximum activity at pH 2.0 and over 50% maximum activity at pH 2.5–4.5. The K m,app and V max,app values for polygalacturonic acid were 1.25 mg/ml and 2526 μmol/min/mg, respectively. When treated apple juice at the concentration of 10 U/ml, endo-PGA1 reduced the intrinsic viscosity (7.7% vs. 8.0%) and increased the light transmittance (84% vs. 86%) almost on the same level as the commercial compound pectinase did. These properties make endo-PGA1 an interesting biocatalyst for acidic industrial processes, especially in the juice clarification.
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