Purification and Characterization of an Acidophilic Xylanase from Aureobasidium pullulans var.melanigenum and Sequence Analysis of the Encoding Gene

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An extracellular endo-1, 4-β-xylanase was purified from the culture supernatant of Aureobasidium pullulans var.melanigenum(ATCC 20524)grown on oat-spelt xylan. The purified enzyme showed a single band on SDS-polyacrylamide gel electrophoresis with an apparent M_r of 24kDa and had an isoelectric point of 6.7. Xylanase activity was optimal at pH2.0 and 50℃. The genomic DNA and cDNAs encoding this protein were cloned and sequenced. Southern blot analysis indicated that the xylanase gene(xynI)was present as a single copy in the genome. An open reading frame, consisting of 663bp, encoded a presumed prepropeptide of 34 amino acids and a mature protein of 187 amino acid. The DNA region encoding the prepeptide was interrupted by a 59-bp intron. A single transcription start point was observed at position -46(A)from the start codon. The 5'-noncoding region had a putative TATA box at -91(TATATAA)and two possible CCAAT boxes at -247(CAAT)and -283(CCAAT). A cloned xynI cDNA was expressed in Saccharomyces cerevisiae. The deduced amino acid sequence showed 94% identity with that of a previously reported equivalent gene(xynA)encoding a xylanase with an optimal pH of 4.8 from a color variant strain, NRRL Y-2311-1, of A.pullulans. A neighbor-joining tree showed that the Aureobasidium enzymes are closely related to several other family-11 xylanases from black aspergilli and Penicillium purpurogenum.
社団法人日本生物工学会の論文
2001-09-25