Activity and substrate specificity of lytic polysaccharide monooxygenases: An ATR FTIR-based sensitive assay tested on a novel species from Pseudomonas putida

Pseudomonas putida W619 is a soil Gram-negative bacterium commonly used in environmental studies thanks to its ability in degrading many aromatic compounds. Its genome contains several putative carbohydrate-active enzymes such as glycoside hydrolases and lytic polysaccharide monooxygenases (PMOs). In this study, we have heterologously produced in Escherichia coli and characterized a new enzyme belonging to the AA10 family, named PpAA10 (Uniprot: B1J2U9), which contains a chitin-binding type-4 module and showed activity toward beta-chitin. The active form of the enzyme was produced in E. coli exploiting the addition of a cleavable N-terminal His tag which ensured the presence of the copper-coordinating His as the first residue. Electron paramagnetic resonance spectroscopy showed signal signatures similar to those observed for the copper-binding site of chitin-cleaving PMOs. The protein was used to develop a versatile, highly sensitive, cost-effective and easy-to-apply method to detect PMO's activity exploiting attenuated total reflection-Fourier transform infrared spectroscopy and able to easily discriminate between different substrates.