Effect of inhibition of proteasome-mediated proteolysis on ligninolytic activities of white-rot fungi

It has recently been established that most short- and long-lived cellular proteins (80-90%) are degraded by a highly selective non-lysosomal pathway that requires ATP and a large (-2.5 MDa) multisubunit, multicatalytic proteinase complex known as the 26S proteasome. It degrades many important proteins involved in signaling pathway, in cell cycle control, and in general metabolism, including transcription factors and key metabolic enzymes. Here, we demonstrated all distinct proteasome activities: chymotrypsinlike, trypsin-like, and caspase-like (peptidylglutamyl-peptide hydrolyzing) in mycelial extracts of the white-rot fungi Trametes versicolor and Phlebia radiata by monitoring cleavage of three different fluorogenic peptide substrates: Suc-LLVY-MCA, Z-GGR-MCA, Z-LLE-βSNA, respectively. We also found that this cleavage was ATP-dependent. Reagents that inhibit proteasome-mediated protein degradation in intact cells have recently become available, including substrate-related peptide aldehydes. These inhibitors are useful tools to demonstrate that a process exhibits proteasome-dependent biochemical regulation. In the present study, we report that in vivo Cbz-LLLal treatment strongly inhibited all tested proteasome activities and affected ligninolytic activities in nutrient deprived cultures of both fungi.