= RGD motif
{c}
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.<Cell attachment activity of fibronectin can be duplicated by small synthetic fragments of the molecule by M. D. Pierschbacher and E. Ruoslahti>[Abstract: L-arginyl-glycyl-L-aspartyl-L-serine and the attachment domain]{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>.
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