The C terminus of liprin-α1 positions liprin-α1 and localizes insulin granule fusion to the ECM interface. (A) Schematic of the domain organization of liprin-α1 and the residues encoding the GFP-tagged liprin-α1 constructs. Liprin-α1 consists of an N-terminal coiled-coil domain and a C-terminal region comprised of three sterile alpha motif (SAM) domains. (B) Mouse β cells were infected with adenovirus encoding each liprin-α1 construct. Western blot showing level of liprin-α1–FL and liprin-α1–N overexpression levels (∼17X) compared with endogenous liprin-α1. (C and D) Immunofluorescence staining of liprin-α1 constructs (green) in isolated mouse β cells (insulin; blue) grown on coverslips coated with laminin-511, at the laminin-cell interface (bottom) compared with the middle. A line scan plotting fluorescence intensity across an orthogonal section (XZ) shows local enrichment of liprin-FL, but not liprin-N, at the laminin-cell interface. (E and F) Glucose-stimulated insulin secretion, normalized to total cellular insulin content, was comparable in β cells overexpressing GFP (control), liprin-FL, and liprin-N. (F) Expression of the N-terminal construct after liprin-α1 knockdown rescued secretion (for each condition, n = 3 animals; two-way ANOVA followed by Tukey’s multiple comparison, *: P < 0.05). (G–I) Isolated β cells overexpressing liprin-FL and liprin-N, cultured on laminin-511, were imaged using live-cell two-photon microscopy. Granule fusion was biased toward the coverslip in β cells expressing liprin-FL but not liprin-N. All scale bars: 10 μm, unless specified. All data are shown as mean ± SEM. Source data are available for this figure: SourceData F3.