Identification and characterization of an acidic and acid-stable endoxyloglucanase from Penicillium oxalicum

Abstract

Xyloglucan is a major structural macromolecule of the primary cell wall of spermatophytes. The hydrolysis of xyloglucan by xyloglucanases may facilitate the hydrolysis of cellulose by cellulases, which is beneficial for bioethanol production. Penicillium oxalicum has been employed for commercial cellulase production. In P. oxalicum, many genes and proteins related to the degradation of structural macromolecules of the plant cell wall have been found, but no gene encoding a xyloglucanase has been identified. In this study, a gene, PoxXEG12A, was cloned from P. oxalicum and expressed in Pichia pastoris, and the gene product was enzymatically characterized. PoxXEG12A shared 63% sequence identity with endoxyloglucanases from Aspergillus niger and Aspergillus aculeatus. PoxXEG12A specifically hydrolyzed tamarind xyloglucan in endo-acting mode and, thus, it is an endoxyloglucanase. PoxXEG12A was most active at pH 4.5⿿5.5 and at 55⿿60°C, with a specific activity of 172U/mg protein toward tamarind xyloglucan. The enzyme was stable at pH 3.5⿿7.0 and below 40°C. The properties of the endoxyloglucanase PoxXEG12A suggest that the enzyme might have potential in industrial applications.