Lytic Polysaccharide Monooxygenases (LPMOs) oxidatively cleave recalcitrant polysaccharides like cellulose and chitin present in the plant cell walls. Although poorly understood, the generally accepted mechanism of LPMO catalysis include reduction of the Cu, polysaccharide binding, binding of oxygen species, and glycosidic bond cleavage. The active site or the primary coordination sphere of an LPMO is formed by the highly conserved Histidine-brace. The neighboring area constitutes the secondary co-ordination sphere, which is proposed to stabilize the oxygen species, intermediates and take part in proton transfer. In the AA9 family LPMOs, a histidine at this site has been proposed to be a potential proton donor. In this video, the protonation state of this conserved histidine in AA9 family LPMOs was investigated by carrying out partial unrestrained refinement of high resolution crystal structures and calculation of the subsequent histidine ring geometry. The video shows that this histidine is generally singly protonated and unlikely to play the role as a proton donor during catalysis.