 RGD motif

The RGD motif is the three-amino acid sequence arginine–glycine–aspartic acid, abbreviated R–G–D in one-letter notation. In fibronectin, this sequence contributes to cell adhesion and recognition by integrins. A protein primary structure can therefore contain a short recognizable region whose activity depends on its molecular presentation.

The originating 1984 experiment measured attachment-promoting activity of synthetic fragments from fibronectin. Its reported active sequence was the four-residue peptide RGDS, with serine following the RGD motif. The three-letter name of the core and the four-residue experimental fragment must be kept distinct.^[ref]

For an original sequence example, the invented five-residue string ARGDS contains the RGD motif at positions 2–4; ARGES does not. The two strings have equal length, but substituting glutamic acid for aspartic acid changes their local sequence. This inspection identifies a motif, not an experimentally established attachment activity. A folded protein, a surface-presented peptide and a soluble peptide present different physical contexts; the activity of one preparation does not specify every function of full-length fibronectin.