Carbohydrate-binding property of a cell wall integrity and stress response component (WSC) domain of an alcohol oxidase from the rice blast pathogen Pyricularia oryzae

The cell wall integrity and stress response component (WSC) domain was first described in the Wsc-family protein of the yeast Saccharomyces cerevisiae, and later found in diverse eukaryotic organisms. Due solely to their presence in the Wsc-family proteins working as a plasma membrane sensor for surface stress and in a fungal β-1,3-exoglucanse, WSC domains have been presumed to possess carbohydrate-binding property without any experimental evidence. Aiming at elucidation of function(s) of WSC domains, we characterized a WSC domain-containing alcohol oxidase from the rice blast pathogen Pyricularia oryzae (PoAlcOX). Recombinant PoAlcOX produced with Pichia pastoris showed alcohol oxidase activity toward a wide range of substrates including two aliphatic alcohols, a branched-chain alcohol, a diol, and a polyol. Deletion of the WSC domain virtually unaffected oxidation of these substrates by PoAlcOX, indicating that the domain makes no contribution to the catalytic activity. In analogy to some carbohydrate-binding modules, we inferred that the WSC domain plays a role in protein anchoring, and evaluated binding capability of PoAlcOX to a set of polysaccharide components of fungal and plant cell walls. This revealed that PoAlcOX binds to xylans and fungal chitin/β-1,3-glucan in the WSC domain-dependent manner, demonstrating for the first time the carbohydrate-binding property of the domain. Additionally, we provide evidence that PoAlcOX immobilized on birch wood xylan retains the catalytic activity. Overall, the data we collected suggest that the role of the WSC domain of PoAlcOX is not recognition of substrates but attaching the enzyme to plant and/or fungal cell wall.