Meprin, A5 protein, and protein tyrosine phosphatase Mu (MAM) domain. MAM is an extracellular domain which mediates protein-protein interactions and is found in a diverse set of proteins, many of which are known to function in cell adhesion. Members include: type IIB receptor protein tyrosine phosphatases (such as RPTPmu), meprins (plasma membrane metalloproteases), neuropilins (receptors of secreted semaphorins), and zonadhesins (sperm-specific membrane proteins which bind to the extracellular matrix of the egg). In meprin A and neuropilin-1 and -2, MAM is involved in homo-oligomerization. In RPTPmu, it has been associated with both homophilic adhesive (trans) interactions and lateral (cis) receptor oligomerization. In a GPI-anchored protein that is expressed in cells in the embryonic chicken spinal chord, MDGA1, the MAM domain has been linked to heterophilic interactions with axon-rich region.