Lytic polysaccharide monooxygenase (LPMO) are mononuclear copper enzymes of importance to industrial bioconversion of lignocellulose (Johansen). The bacterial Cu binding proteins CopC share a similar mononuclear Cu site. This site is defined by an N-terminal histidine and a second internal histidine side chain in a configuration called the histidine brace. However, whereas LPMOs are able to break very strong C-H bonds in the carbohydrate substrates during catalysis, CopC functions as a non-catalytic copper chaperone. We have recently identified LPMO-like proteins based on their amino acid sequence similarity that define a family of proteins named X235. The fold of these proteins resembles LPMOs but they share CopC features at the Cu-site. One, Bim1 from Cryptococcus neoformans, is a critical factor in Cu acquisition in fungal meningitis (Garcia-Santamarina, Probst et al.). Another, X325 member from the ectomycorrhizal fungus Laccaria bicolor is found at the interface between fungal hyphae tree rootletcells (Labourel, Frandsen et al.). No polysaccharide cleaving activity was detected for these LPMO-like proteins .
An unpublished comparative study of the structural and biochemical properties of a well-described cellulose-specific LPMO from Thermoascus aurantiacus (TaAA9A) (Quinlan, Sweeney et al.), CopC from Pseudomonas fluorescens, and Bim1 from Cryptococcus neoformans was carried out and the data will be presented. These three biologically relevant examples emphasize how the proteinaceous environment control reactivity of Cu with O2.