Molecular cloning and sequence analysis of two endoinulinase genes from Aspergillus niger

Two genomic DNAs encoding endoinulinase from Aspergillus niger 12 were cloned and sequenced. Open reading frames (ORFs) of the endoinulinase genes, inuA and inuB, both consisted of 1,548 nucleotides encoding 516 amino acids. It was suggested that the coding regions were not interrupted by introns. The ORFs differed from each other by 23 nucleotide substitutions or by eight amino acid replacements, indicating that the inuA and inuB genes arose by gene duplication. Each mature enzyme of 493 amino acids was preceded by a hydrophobic signal peptide of 23 amino acids. The enzymes contained two Cys residues and five potential sites for N-linked glycosylation. Partial amino acid sequences of the secreted enzyme suggested that it originated from the inuB gene product. The deduced amino acid sequences of the mature A. niger enzymes showed 73% identity with that of the Penicillium purpurogenum endoinulinase.