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Publication Abstract from PubMed

Fungal polysaccharide monooxygenases (PMOs) oxidatively degrade cellulose and other carbohydrate polymers via a mononuclear copper active site using either O(2) or H(2)O(2) as a cosubstrate. Cellulose-active fungal PMOs in the auxiliary activity 9 (AA9) family have a conserved second-sphere hydrogen-bonding network consisting of histidine, glutamine, and tyrosine residues. The second-sphere histidine has been hypothesized to play a role in proton transfer in the O(2)-dependent PMO reaction. Here the role of the second-sphere histidine (H157) in an AA9 PMO, MtPMO9E, was investigated. This PMO is active on soluble cello-oligosaccharides such as cellohexaose (Glc6), thus enabling kinetic analysis with the point variants H157A and H157Q. The variants appeared to fold similarly to the wild-type (WT) enzyme and yet exhibited weaker affinity toward Glc6 than WT (WT K(D) = 20 +/- 3 muM). The variants had comparable oxidase (O(2) reduction to H(2)O(2)) activity to WT at all pH values tested. Using O(2) as a cosubstrate, the variants were less active for Glc6 hydroxylation than WT, with H157A being the least active. Similarly, H157Q was competent for Glc6 hydroxylation with H(2)O(2), but H157A was less active. Comparison of the crystal structures of H157Q and WT MtPMO9E reveals that a terminal heteroatom of Q157 overlays with N(epsilon) of H157. Altogether, the data suggest that H157 is not important for proton transfer, but support a role for H157 as a hydrogen-bond donor to diatomic-oxygen intermediates, thus facilitating catalysis with either O(2) or H(2)O(2).

Second-Sphere Histidine Catalytic Function in a Fungal Polysaccharide Monooxygenase.,Batka AE, Thomas WC, Tudorica DA, Sayler RI, Marletta MA Biochemistry. 2024 Dec 3;63(23):3136-3146. doi: 10.1021/acs.biochem.4c00527. Epub , 2024 Nov 20. PMID:39563485^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.