Plays a role in coupling actin fibers to cell junctions in endothelial cells, via its interaction with AMOTL2 and CDH5 (By similarity). May regulate acid-induced ASIC3 currents by modulating its expression at the cell surface (By similarity). {ECO:0000250, ECO:0000250|UniProtKB:Q6RHR9}. This is the function of Ensembl gene identifier ENSG00000151276 (MAGI1, membrane associated guanylate kinase, WW and PDZ domain containing 1).