Sequence Analysis and Heterologous Expression of Polygalacturonase Gene (AspecA) from a Shoyu Koji Mold, Aspergillus sojae KBN1340

A polygalacturonase gene designated as AspecA was isolated from a shoyu koji mold, Aspergillus sojae KBN1340, and characterized. The structural gene comprised 1,226 bp with two introns. The open reading frame encoded a 363-residue protein with a signal peptide of 28 residues. AspecA shared a high degree of sequence identity with Aspergillus parasiticus pecA, Aspergillus oryzae pgaA and Aspergillus flavus pecA. Utilizing the promoter of the A. oryzae taaG2 gene and its signal peptide, AsPecA was successfully expressed in A. oryzae and secreted into the culture medium. AsPecA had a molecular mass of 36.0 kDa, a pH optimum of 5.0, and a temperature optimum of 50 degrees C.