Phosphorylation cycles on vesicles

Clathrin-coated vesicles (CCVs) that traffic between the trans-Golgi network and endosomes are nucleated by the adaptor protein complex-1 (AP-1). AP-1 sorts and packages cargo into CCVs and then falls off the vesicles before they arrive at their destination. On page 699, Ghosh and Kornfeld demonstrate that two of the four AP-1 subunits are opposingly phosphorylated and dephosphorylated. The regulatory cycles control vesicle trafficking by turning on cargo recruitment and clathrin coating at the appropriate time.

Cargo recruitment is mediated by the μ1 subunit of AP-1. The authors demonstrate that μ1 is phosphorylated on the membrane and dephosphorylated in the cytosol. Phosphorylation induced a conformational change in μ1 that increased its affinity for cargo ligands. Addition of a phosphate group also alters the conformation of the μ2 subunit of AP-2, which regulates...