beta2adaptin

Beta-2 adaptin, also known as the beta-2 subunit of adaptor protein complex 2 (AP-2), is a cytosolic protein encoded by the AP2B1 gene in humans. It is one of four subunits of the clathrin adaptor AP-2 complex, the others being alpha-adaptin, mu2-adaptin, and sigma2-adaptin. The AP-2 complex functions at the plasma membrane to drive clathrin-mediated endocytosis by recognizing sorting signals on cargo proteins and linking them to the clathrin coat, enabling vesicle formation.

Beta-2 adaptin contributes to coat assembly by forming part of the core AP-2 complex and by binding to clathrin heavy chain. It cooperates with the other subunits to stabilize membrane association and to recruit clathrin triskelia and accessory factors to sites of endocytosis. The complex binds to cargo via motifs such as YXXφ and dileucine signals, with the mu2 subunit primarily responsible for cargo recognition; beta-2 adaptin supports this process through structural contacts and membrane targeting, including interactions with phosphoinositide-enriched membranes.

Disruption of AP-2 function, including beta-2 adaptin, impairs clathrin-mediated endocytosis and affects trafficking of membrane receptors such as the transferrin receptor and other cargo proteins. The AP-2 complex is conserved across animals, with AP2B1 as the human beta-2 adaptin gene. Beta-2 adaptin has no catalytic activity but serves as a scaffold for assembly and cargo selection in clathrin-coated vesicle formation.