HAX-1: Proteins and Enzymes

HAX-1 (HCLS1-associated protein X-1; also HS1-binding protein1) is a 34-35 kDa intracellular protein with structural similarity to Bcl-2 family proteins. It is ubiquitously expressed, and participates in a variety of cell-specific functions. HAX-1 blocks cardiomyocyte apoptosis via caspase-9 inhibition, downregulates conjugated bile acid secretion via BSEP binding, and via PKD2, transmitts integrin signals to the ER. Human HAX-1 is 279 amino acids (aa) in length and contains two Bcl-2 homology regions (aa 37-56 and 74-89), a PEST domain (aa 104-117) and a potential transmembrane segment (aa 261-279). HS-1 is found mostly in the mitochondria. HAX-1 is also cleaved by caspase-3 at Asp127. Over aa 2-261, human HAX-1 shares 81% aa identity with mouse HAX-1.