AP2

AP2 is an abbreviation used for several topics in biology and related fields. The most widely known usage is for the adaptor protein complex 2 (AP-2), a key component of clathrin-mediated endocytosis.

The AP-2 adaptor complex is a heterotetramer consisting of two large adaptin subunits (alpha-adaptin and beta2-adaptin), a medium subunit (mu2), and a small subunit (sigma2). It functions at the plasma membrane to select cargo proteins for internalization by recognizing sorting signals such as YXXΦ and dileucine motifs via the mu2 and sigma2 subunits. Recruitment to the membrane is aided by binding to phosphatidylinositol 4,5-bisphosphate (PIP2). The complex can switch from a closed to an open conformation upon cargo engagement, enabling interaction with clathrin and other accessory factors to form clathrin-coated pits and vesicles. It plays a central role in the endocytosis and trafficking of receptors, transporters, and other membrane proteins. Regulation occurs through phosphorylation, cargo load, and interactions with other proteins, and disruptions can affect signaling pathways and have been linked to various diseases and to routes used by some pathogens for entry.

In plants, AP2 refers to the APETALA2 family of transcription factors, members of the AP2/ERF superfamily. These proteins regulate key developmental processes such as flower and seed development and also participate in responses to abiotic and biotic stress. They contain AP2 DNA-binding domains and function as transcriptional regulators within broader developmental networks.

In other contexts, AP2 can denote additional system-specific or organizational identifiers; see disambiguation for details.