Scaffold protein that connects plasma membrane proteins with members of the ezrin/moesin/radixin family and thereby helps to link them to the actin cytoskeleton and to regulate their surface expression. Necessary for recycling of internalized ADRB2. Was first known to play a role in the regulation of the activity and subcellular location of SLC9A3. Necessary for cAMP-mediated phosphorylation and inhibition of SLC9A3. May enhance Wnt signaling (By similarity). May participate in HTR4 targeting to microvilli. Involved in the regulation of phosphate reabsorption in the renal proximal tubules (By similarity). Involved in sperm capacitation. May participate in the regulation of the chloride and bicarbonate homeostasis in spermatozoa. Homodimer, and heterodimer with SLC9A3R2. Binds the N-termini of EZR, RDX and MSN. Binds the C-termini of PDGFRA, PDGFRB, ADRB2 and NOS2. Binds ARHGAP17, EPI64, RACK1, OPRK1, GNAQ, CTNNB1, PLCB3 and CLCN3. Forms a complex with CFTR and SLC4A7. Forms a complex with SLC4A7 and ATP6V1B1 (By similarity). Binds PDZK1. Binds the C-terminus of PAG1. In resting T-cells, part of a PAG1-SLC9A3R1-MSN complex which is disrupted upon TCR activation. Directly interacts with HTR4. Interacts with MCC (By similarity). Interacts with TRPC4 (via the PDZ-binding domain) (By similarity). Interacts (via the PDZ 1 domain) with PODXL (via the C-terminal PDZ-binding motif DTHL); interaction is not detected in glomerular epithelium cells (By similarity). Interacts (via the PDZ 1 domain) with PODXL (via the C-terminal PDZ-binding motif DTHL); the interaction take place early in the secretory pathway and is necessary for its apical membrane sorting (By similarity). Interacts with SLC34A1 (By similarity). Interacts with CFTR, SLC26A3 and SLC26A6. Interacts (via PDZ domains) with ACE2 (via PDZ-binding motif); the interaction may enhance ACE2 membrane residence (By similarity). Colocalizes with actin in microvilli-rich apical regions of the syncytiotrophoblast. Present in lipid rafts of T-cells (By similarity). Translocates from the cytoplasm to the apical cell membrane in a PODXL-dependent manner. Colocalizes with CFTR at the midpiece of sperm tail. Expressed in spermatogenic cells.