Acid Xylanase from Yeast Cryptococcus sp. S-2: Purification, Characterization, Cloning, and Sequencing

Abstract

A xylan-degrading enzyme produced by yeast Cryptococcus sp. S-2 was isolated and purified, and characterized as an endoxylanase (1, 4-β-D-xylan xylanohydrolase [EC 3.2.1.8]). We estimated the molecular weight and isoelectric point of purified xylanase (xyn-CS2) to be 22, 000 and 7.4, respectively. This low-molecular-weight xylanase had an unusual pH optimum of 2.0, and showed 75% of maximal activity even at pH 1.0. An open reading frame of the cDNA specified 209 amino acids, including a putative signal peptide of 25 amino acids. The deduced amino acid sequence of xyn-CS2 shared significant similarities with the family-G xylanases of B. pumilus, C acetobutylicum, T reesei, and A. kawachii. Xyn-CS2 included two unique cysteine residues in a putative catalytic region, raising the possibility that these residues are at least partially responsible for its acidophilic nature.