Saprophytic fungi degrade lignocellulosic polymers present in plant cell walls using dedicated lignocellulosic enzymes such as ‘Carbohydrate Active enZYmes’ (CAZYmes) and peroxidases. These enzymes are secreted in the extracellular environment together with reactive oxygen species (ROS), shown to participate actively to vegetal biomass degradation. Numerous CAZYmes are routinely used in biotechnology approaches and understand their functioning is of crucial importance to improve and create new ways of biomass valorization. ROS can oxidize proteins on sensitive amino acids leading to post-translational modifications (PTMs), the consequences of which range from damaging effects to fine-tuned regulation of protein functions and fates. For example, the reversible oxidation of methionine into methionine sulfoxyde (MetO) can act as redox switch to regulate proteins involved in several cell functions. If the effects of ROS on numerous proteins of bacteria, plants or animals have been studied, almost nothing is known about fungal proteins and specifically during biomass degradation. Our study aims to identify and characterize proteins carrying MetO, that are secreted during biomass degradation in fungi. We chose Pycnoporus cinnabarinus as a model basidiomycete capable of producing a large arsenal of lignocellulosic enzymes. A chemoproteomic approach is being used with first the synthesis of an oxaziridine probe targeting redox-sensitive Met. The labeling of Met by this chemical probe has been validated in a model protein. Coupled to a mass spectrometry analysis, this probe will then allow us to identify proteins carrying redox-active Met. The effect of redox modification of Met will then be elucidated on recombinant proteins. This approach should help to uncover redox regulated CAZYmes.