AP5M1

MuD consists of 490 amino acids that interact to form a tertiary structure with three domains.[11][12]

The overall structure shares similarities with adaptor protein (AP) complexes that are related to clathrin-mediated endocytosis; amino acids 197 through 417 are a shared adaptin domain found in AP μ subunits.[13][14]

Within the adaptin domain are two aspartic acids, D276 and D290, which serve as binding sites for caspase-3.[14]

The overall function of MuD remains unclear.[15] It is known, however, that MuD regulates the expression of BAX, a pro-apoptotic member of the Bcl-2 family of proteins.[16][15] Due to— and dependent upon— this relationship, MuD has been able to induce cell death in tumor cells.[17][16][15]

Additionally, MuD has been suggested to be involved in endosomal trafficking.[17][16][18][15]

TRAIL, an apoptosis-inducing ligand, activates caspase-8 and caspase-3, which initiate the intrinsic pathway of apoptosis by cleaving BH3 interacting-domain death agonist (Bid) into tBid, another pro-apoptotic member of the Bl-2 protein family.[19][20][21][22] MuD interferes with this process because D276 and D290 act as alternative binding sites for caspase-3, decreasing the amount of Bid that gets cleaved.[20][19][21] Tumor cells being treated with TRAIL are 32% more likely to survive when MuD is being expressed.[19]