The AP2S1 antibody targets the Adaptor Protein 2 Sigma subunit 1 (AP2S1), a critical component of the heterotetrameric AP-2 complex involved in clathrin-mediated endocytosis (CME). AP2S1. encoded by the AP2S1 gene, is the smallest subunit (17 kDa) of the AP-2 complex, which facilitates cargo recognition, membrane recruitment, and clathrin-coated vesicle formation during receptor internalization. Structurally, AP2S1 contains an N-terminal α-helix and a C-terminal σ2 domain that interacts with YxxΦ motifs in cargo proteins. Dysregulation of AP2S1 has been linked to disorders of calcium homeostasis, particularly familial hypocalciuric hypercalcemia type 3 (FHH3), caused by gain-of-function mutations affecting calcium-sensing receptor (CaSR) trafficking. AP2S1 antibodies are widely used in research to study AP-2 complex assembly, endocytic mechanisms, and CaSR-related pathologies. They are employed in techniques like Western blotting, immunofluorescence, and immunoprecipitation to assess protein expression, subcellular localization, and functional interactions. Commercial AP2S1 antibodies are typically raised against epitopes in the σ2 domain, validated for specificity across human, mouse, and rat models. Recent studies also explore AP2S1's role beyond endocytosis, including signaling pathways and neurological functions, making these antibodies valuable tools for both basic and translational research.