Structural and inhibitory properties of a plant proteinase inhibitor containing the RGD motif

Purified from Bauhinia rufa seeds, BrTI is a Kunitz proteinase inhibitor that contains the RGD sequence. BrTI inhibits trypsin (Kiapp 2.9 nM) and human plasma kallikrein (Kiapp 14.0 nM) but not other related enzymes. The synthetic peptide YLEPVARGDGGLA-NH2 (70 μM) inhibited the adhesion to fibronectin of B16F10 (high-metastatic B16 murine mouse melanoma cell line) and of Tm5 (murine melanoma cell lines derived from a non-tumorigenic lineage of pigmented murine melanocytes, melan-a). YLEPVARGEGGLA-NH2 in which Asp9 was changed into Glu does not affect the cell attachment. Moreover, this peptide was functional only when the sequence present in the native protein was preserved, since YLIPVARGDGGLA-NH2 in which Glu3 was changed into Ile does not interfere with B16F10 and was less effective on Tm5 cell line adhesion. Neither YLEPVARGDGGLA-NH2, YLIPVARGDGGLA-NH2 or YLEPVARGEGGLA-NH2 inhibit the interaction of RAEC (endothelial cell line from rabbit aorta) with fibronectin.