Abstract Integrin clusters facilitate mechanical force transmission (mechanotransduction) and regulate biochemical signaling during cell adhesion. However, most studies have focused on rigid substrates. On fluid substrates like supported lipid bilayers (SLBs), integrin ligands are mobile, and adhesive complexes are traditionally thought unable to anchor for cell spreading. Here, we demonstrate that cells spread on SLBs coated with Invasin, a high-affinity integrin ligand.