Acts probably as a receptor for selective autophagosomal degradation of ubiquitinated targets. Homooligomer and heterooligomer. Interacts with RNF29, USP8, SQSTM1, MAP1LC3A, MAP1LC3B, MAP1LC3C, GABARAP, GABARAPL1 and GABARAPL2 (By similarity). Binds to ubiquitin and ubiquitinated proteins (By similarity). Interacts with SQSTM1, titin/TTN and TRIM55. In cardiac muscles localizes to the sarcomeric M line (PubMed:15802564). Is targeted to lysosomes for degradation (By similarity). The PB1 domain mediates interaction with SQSTM1.