CHC22 clathrin recruitment to the early secretory pathway requires two-site interaction with SNX5 and p115

The two clathrin isoforms, CHC17 and CHC22, mediate separate intracellular transport routes. CHC17 performs endocytosis and housekeeping membrane traffic in all cells. CHC22, expressed most highly in skeletal muscle, shuttles the glucose transporter GLUT4 from the ERGIC (endoplasmic-reticulum-to-Golgi intermediate compartment) directly to an intracellular GLUT4 storage compartment (GSC), from where GLUT4 can be mobilized to the plasma membrane by insulin. Here, molecular determinants distinguishing CHC22 from CHC17 trafficking are defined. We show that the C-terminal trimerization domain of CHC22 interacts with SNX5, which also binds the ERGIC tether p115. SNX5, and the functionally redundant SNX6, are required for CHC22 localization independently of their participation in the endosomal ESCPE-1 complex. In tandem, an isoform-specific patch in the CHC22 N-terminal domain separately mediates binding to p115. This dual mode of clathrin recruitment, involving interactions at both N- and C-termini of the heavy chain, is required for CHC22 targeting to ERGIC membranes to mediate the Golgi-bypass route for GLUT4 trafficking. Interference with either interaction inhibits GLUT4 targeting to the GSC, defining a bipartite mechanism regulating a key pathway in human glucose metabolism. Synopsis The formation of insulin-sensitive GLUT4-containing compartments involves direct secretion that bypasses the Golgi apparatus and uses the dedicated clathrin isoform CHC22. This study defines two key interactions between CHC22 and the early secretory tether p115 in this process; direct binding by the CHC22 N-terminal domain and indirectly through SNX5/6 bound to the CHC22 trimerization domain. Sorting nexin 5/6 (SNX5/6) levels influence CHC22 clathrin’s membrane localization. SNX5 binds the early secretory pathway protein p115. The terminal domain (TD) of CHC22 clathrin contains an isoform-specific divergent patch that binds p115. CHC22 direct binding to p115 via the TD and binding to SNX5/6 are required for association with the early secretory pathway. The two-site interaction of CHC22 with p115 is required for appropriate trafficking of the insulin-responsive glucose transporter GLUT4. Insulin-responsive GLUT4 secretion requires a designated clathrin isoform, CHC22, which is specifically recruited through its interactions with the trafficking proteins p115 and SNX5.