Alix (ALG-2-interacting protein X) is an adaptor protein that was first described for its capacity to bind to the calcium-binding protein ALG-2, the expression of which seemed necessary for cell death. Predicted molecular weight approximately 96kD. Alix contains an N-terminal Bro1 domain and a C-terminal proline-rich domain (PRD). The PRD contains multiple polyproline motifs, which are potential docking sites for proteins containing SH3 domains, interact with multiple cellular Alix-binding partners that are involved in apoptotic induction, endosomal sorting, and endocytosis. Bro1 domain interacts with CHMP4b which is also involved in endosomal sorting.