SUBCELLULAR TARGETING AND CYTOSKELETAL ATTACHMENT OF SAP97 TO THE EPITHELIAL LATERAL MEMBRANE

The synapse-associated protein SAP97 is a member of a novel family of cortical cytoskeletal proteins involved in the localization of ion cha nnels at such membrane specializations as synaptic junctions. These mu ltidomain proteins have binding sites for protein 4.1, GKAPs/SAPAPs, v oltage- and ligand-gated ion channels and cell-adhesion molecules cont aining C-terminal T/SXV motifs. In this study, we evaluated the contri bution of individual domains in SAP97 to its selective recruitment and attachment to the cortical cytoskeleton in epithelial cells, We find that the PDZ, SH3 and GK domains, as well as the I3 insert in SAP97, a re not essential for subcellular targeting, though both PDZ1-2 domains and the I3 insert affect the efficiency of localization, Instead, we show that the first 65 amino acid residues in SAP97, which are absent from SAP90/PSD-95 and SAP102, direct the selective subcellular localiz ation and can mediate at least one point of attachment of SAP97 to the cytoskeleton assembled at sites of cell-cell contact. Our data demons trate that it is the sequences unique to SAP97 that direct its subcell ular targeting to the epithelial lateral membrane.