Applied Microbiology and Biotechnology, Vol.104, No.20, 8761-8773, 2020
Identification and characterization of two xyloglucan-specific endo-1,4-glucanases inAspergillus oryzae
Aspergillus oryzaeproduces glycoside hydrolases to degrade xyloglucan. We identified and characterized two xyloglucan-specific endo-1,4-glucanases (xyloglucanases) named Xeg12A and Xeg5A. Based on their amino acid sequences, Xeg12A and Xeg5A were classified into glycoside hydrolase families GH12 and GH5, respectively. Xeg12A degrades tamarind seed xyloglucan polysaccharide into xyloglucan oligosaccharides containing four glucopyranosyl residues as main chains, including heptasaccharides (XXXG: Glc(4)Xyl(3)), octasaccharides (XXLG and XLXG: Glc(4)Xyl(3)Gal(1)), and nonasaccharides (XLLG: Glc(4)Xyl(3)Gal(2)). By contrast, Xeg5A produces various xyloglucan oligosaccharides from xyloglucan. Xeg5A hydrolyzes xyloglucan into not only XXXG, XXLG/XLXG, and XLLG but also disaccharides (isoprimeverose: Glc(1)Xyl(1)), tetrasaccharides (XX: Glc(2)Xyl(2)and LG: Glc(2)Xyl(1)Gal(1)), and so on. Xeg12A is a typical endo-dissociative-type xyloglucanase that repeats hydrolysis and desorption from xyloglucan. Conversely, Xeg5A acts as an endo-processive-type xyloglucanase that hydrolyzes xyloglucan progressively without desorption. These results indicate that although both Xeg12A and Xeg5A contribute to the degradation of xyloglucan, they have different modes of activity toward xyloglucan, and the hydrolysis machinery of Xeg5A is unique compared with that of other known GH5 enzymes.