STRUCTURAL AND FUNCTIONAL-CHARACTERIZATION OF VITRONECTIN-DERIVED RGD-CONTAINING PEPTIDES FROM HUMAN HEMOFILTRATE

Bioactive peptides derived from the adhesive plasma protein vitronecti n are present at submicromolar concentrations in human hemofiltrate of patients with renal diseases and were isolated by a combination of hi gh-efficiency chromatographic steps. The structural and functional pro perties of these peptides were characterized. Sequencing and mass spec trometry revealed the existence of peptide isoforms (5-6 kDa) which co rresponded to the N-terminus (residues 1 to 44-50) of vitronectin. The isolated peptides bound directly to plasminogen-activator inhibitor-1 (PAI-1) and were effective competitors of the interaction of PAI-1 wi th isolated intact vitronectin or extracellular matrix. These function al properties were indistinguishable from the binding properties of a recombinant fusion protein containing residues 1-52 of vitronectin lin ked to a portion of glutathione S-transferase, expressed in Escherichi a coli. Peptides containing the RGD sequence of vitronectin competed f or vitronectin binding to the alpha v beta 3 integrin. No indication f or direct growth-factor binding was noted, whereas natural peptides we re found associated with PAI-1 as the major binding protein in plasma. These data demonstrate that functionally active vitronectin-derived p eptides are released by unknown protease(s) from the mature protein an d that these peptides are identical, in terms of activity, to recombin ant vitronectin fragments. These natural peptides may interact with ac tive PAI-1 in plasma or at extravascular sites and thereby interfere w ith established biological functions of intact vitronectin.