The Role of the Secondary Coordination Sphere in a Fungal Polysaccharide Monooxygenase

Tolysaccliaride motoOxygenases (PMOs) are secreted metalloenzymes that catalyze the oxidative degradation of polysaccharides; in a copper-, oxygen-, and reduetant-dependent manner. CellulpseactiVe fungal: PMOs degrade cellulosic substrates to be utilized as a carbon source for fungal growth To gain insight into the PMO mechanism)the role of conserved.residues into the copper sphere was investigated. Here, we report active-site hydrogenbonding motifs in the secondary copper coordination sphere ofMtPMO3(*), ftoto the ascomytete fungus Kjiceliophthora itheimophila. A series of substitutions: that disrupt this,conserved network are used to interrogate its function. Activity assays; in conjunction with EPR spectroscopy,demonstfate that residues H161 and Q167 are involved in stabilizing bound oxygen, and H=161 appears to -play a role in proton transfer. Additionally,Q167 increases the ligand tiorior strength:of Y169 to the copper via a hydrogen-bonding interaction. Altogether, H161 and Q167 are important for oXygen activation, and,the results are suggestive of a.ecipper-OxY1 active intermediate.