Tetra-anionic porphyrin mimics protein-protein interactions between regulatory particles and the catalytic core, allosterically activating human 20S proteasome.

Decreased proteasome activity is a hallmark of brain and retinal neurodegenerative diseases (Alzheimer's, Parkinson's diseases, glaucoma) boosting the search for molecules acting as proteasome activators. Based on the hypothesis of an electrostatic key code driving catalytic core particle (20S) activation by regulatory particles (RPs), we identified the tetra-anionic meso-Tetrakis(4-sulphonatophenyl)-porphyrin (H2TPPS) as a new activator of human proteasome. By means of an integrated approach, including bioinformatics, enzymatic kinetic analysis, atomic force microscopy, and dynamic docking simulations, we show how binding of H2TPPS affects the closed/open conformational equilibrium of human 20S to ultimately promote substrate gate opening and proteolytic activity. These outcomes support our hypothesis and pave the way to the rational discovery of new proteasome allosteric modulators able to reproduce the key structural elements of regulatory particles responsible for catalytic activation.