Arg-Gly-Asp is the minimal recognition motif through which many integrins bind their extracellular matrix ligands. It was identified in fibronectin, and GRGDSP reproduces the fibronectin cell-binding site with the flanking serine and proline that follow it in the parent protein. It is the most widely used soluble RGD peptide and the usual first choice when the question is whether a process depends on integrin engagement. In solution the peptide competes with matrix ligands for the integrin binding pocket, so the standard application is to block or detach cells from a fibronectin-coated surface. An important caveat from the literature is that this inhibition can be transient: RGD peptides have been reported to only temporarily inhibit cell adhesion to fibronectin, so time course matters and an end-point measurement taken too late may read as no effect. Immobilised rather than soluble RGD has the opposite function, promoting attachment, which is why the same sequence is grafted onto biomaterials and hydrogels to make otherwise inert surfaces adhesive. The peptide is not purely a blocking reagent either. RGD peptides have been shown to trigger rapid intracellular calcium increases and MAPK signalling in cortical neurons, meaning occupancy of the integrin can itself initiate signalling rather than only preventing ligand binding. For attributing an effect to the RGD motif specifically, run the matched GRGESP control (LT1542), which differs by a single methylene group. | 