Participates in the organization of endoplasmic reticulum-plasma membrane contact sites (EPCS) with pleiotropic functions including STIM1 recruitment and calcium homeostasis. Constitutive tether that co-localize with ESYT2/3 tethers at endoplasmic reticulum-plasma membrane contact sites in a phosphatidylinositol lipid-dependent manner. Pre-marks the subset of phosphtidylinositol 4,5-biphosphate (PI(4,5)P2)-enriched EPCS destined for the store operated calcium entry pathway (SOCE). Localizes to endoplasmic reticulum-plasma membrane contact sites (EPCS). Anchored at the ER, PM binding is mediated via GRAM domain and phosphatidylinositol lipid interaction. Localizes to distinct EPCS than GRAMD1A. GRAM domain is required for specific location to endoplasmic reticulum-plasma membrane contact sites (EPCS). Mediates interaction to phosphatidylinositol lipids and binding to plasma membrane.