Supporting data for "Discovery of a Basement Membrane Sensing Mechanism and Pursuit of Its Structural Basis"

Basement membranes are thin sheets of extracellular matrices that support epithelial and endothelial tissues while delivering instructive signals to cells through specific receptor-ligand pairings. Nidogen-1, a ubiquitous basement membrane glycoprotein, is essential for assembling these membranes by linking laminin and collagen IV networks, yet the mechanisms by which cells sense and respond to nidogen-1 remain not fully understood. Here we identify basal cell adhesion molecule (BCAM), a well-known laminin receptor, as a novel, direct, and functional receptor for nidogen-1. Through an unbiased CRISPR activation receptor screen, BCAM emerged as a principal “sensor” of nidogen-1, conferring robust nidogen-1 binding at the cell surface. We confirmed their direct physical interaction in vitro albeit with far weaker affinity than the high-affinity laminin-521-BCAM interaction, but demonstrated a clear functional relevance of their direct engagement to nidogen-1-guided haptotactic migration. This stark contrast indicates cellular context could potentiate the nidogen-1-BCAM interaction, suggesting regulatory mechanisms at play. Parallel efforts to produce recombinant full-length human nidogen-1 for structural studies yielded only trace monomeric material due to severe aggregation and secretion toxicity upon overexpression. Negative-stain electron microscopy of this fraction, nevertheless, confirmed the conserved three-globule dumbbell shape of the intact human molecule seen in previous mouse studies. Our findings uncover a new receptor-ligand axis in basement membrane sensing and reveal how weak interactions can drive potent cellular responses, advancing our understanding of basement membrane biology. Such cues may also influence ECM-driven development and diseases where basement membrane integrity is compromised.