The tripeptide Arg-Gly-Asp (RGD) was originally identified as the sequence within fibronectin that mediates cell attachment, and has been found in numerous proteins, including the integrins, a family of cell-surface proteins, which act as receptors for cell adhesion molecules. A subset of the integrins recognize the RGD motif within their ligands, the binding of which mediates both cell-substratum and cell-cell interactions.
NAPSA is another peptide shown to contain an RGD motif.
D'Souza SE, Ginsberg MH, Plow EF. Arginyl-glycyl-aspartic acid (RGD): a cell adhesion motif. Trends Biochem Sci. 1991 Jul;16(7):246-50. PMID 1926332