Calpain Small Subunit 1/CAPNS1/CAPN4 [MD435R]

Calpains are calcium-dependent cysteine proteinases that are widely distributed in mammalian cells. Calpains operate as heterodimers, comprising a specific large catalytic subunit (calpain 1 and calpain 2), and a regulatory subunit 1 (Calpain small subunit 1, CAPNS1, or CAPN4). This protein associates with the catalytic large subunits of both μ-calpain (Calpain 1) and m-calpain (Calpain 2) to form heterodimeric cysteine proteases that catalyze limited proteolysis of numerous substrates involved in cytoskeletal remodeling, cell migration, and signal transduction. CAPNS1 is essential for embryonic development and is ubiquitously expressed across tissues. Researchers study this regulatory subunit to understand calpain activation mechanisms, calcium-dependent proteolysis in physiological contexts, and pathological conditions including ischemia-reperfusion injury, neurodegeneration, and endoplasmic reticulum stress responses.