Membrane-associated guanylate kinase with inverted orientation (MAGI3) is a novel, 130 kDa guanylate kinase which is part of a family of multi-PDZ domain containing guanylate kinases. These guanylate kinases are localized to epithelial cell tight junctions. MAGI3 and PTEN/MMAC cooperate to modulate the kinase activity of AKT/protein kinase B (PKB). MAGI3 positions the PTEN/MMAC phosphatase to specific subcellular locations that are involved with the regulation of cell proliferation and survival. MAGI3, as well as other proteins in this family, are made up of an N-terminal guanylate kinase domain, followed by a WW domain, named for two conserved tryptophan residues and first identified as two repeats in mouse YAP65, which is them followed by 5 PDZ domains.