Characterization and chemical modulation of p62/SQSTM1/Sequestosome-1 as an autophagic N-recognin

In the Arg/N-degron pathway, single N-terminal (Nt) residues function as N-degrons recognized by UBR box-containing N-recognins that induce substrate ubiquitination and proteasomal degradation. Recent studies led to the discovery of the autophagic Arg/N-degron pathway, in which the autophagic receptor p62/SQSTM1/Sequestosome-1 acts as an N-recognin that binds the Nt-Arg and other destabilizing residues as N-degrons. Upon binding to Nt-Arg, p62 undergoes self-polymerization associated with its cargoes, accelerating the macroautophagic delivery of p62-cargo complexes to autophagosomes leading to degradation by lysosomal hydrolases. This autophagic mechanism is emerging as an important pathway that modulates the lysosomal degradation of various biomaterial ranging from protein aggregates and subcellular organelles to invading pathogens. Chemical mimics of the physiological N-degrons were developed to exert therapeutic efficacy in pathophysiological processes associated with neurodegeneration and other related diseases. Here, we describe the methods to monitor the activities of p62 in a dual role as an N-recognin and an autophagic receptor. The topic includes self-polymerization (for cargo condensation), its interaction with LC3 on autophagic membranes (for cargo targeting), and the degradation of p62-cargo complexes by lysosomal hydrolases. We also discuss the development and use of small molecule mimics of N-degrons that modulate p62-dependent macroautophagy in biological and pathophysiological processes.