The tripeptide Arg-Gly-Asp (RGD) consists of Arginine, Glycine, and Aspartate. It was originally identified as the amino acid sequence within the extracellular matrix protein fibronectin that mediates cell attachment. The RGD cell binding sequence has since been identified in other extracellular matrix proteins, including vitronectin and laminin. The family of membrane proteins known as integrins act as receptors for these cell adhesion molecules via the RGD motif. A subset of the integrins recognize the RGD motif within their ligands, the binding of which mediates both cell-substratum and cell-cell interactions. These integrins include αvβ3, α5β1 and αIIbβ3.