Receptor recognition specificity of plasminogen for the novel plasminogen receptor, Plg‐RKT

Abstract

Plasminogen (Plg) receptors promote Plg activation to arm cells with plasmin to promote both thrombolysis and cell migration. Plg‐RKT is a new type II integral membrane Plg receptor on leukocytes and other tissues. Our objective was to define the recognition specificity of Plg for Plg‐RKT. The C‐terminal peptide of Plg‐RKT was coupled to microtiter wells. Biotinylated Plg was incubated with the immobilized peptide and detected with streptavidin‐HRP. Plg bound to the peptide in a concentration‐dependent manner (IC50=5 nM). In specificity controls, Plg binding was competed by unlabeled Plg and no binding to the reverse peptide was detected. Plg binding was inhibited in a dose‐dependent manner by the soluble peptide, but was not affected by a mutant peptide with the C‐terminal K replaced with A. A peptide with the proximal upstream R replaced with K was a more effective competitor than the wild type peptide. Human Plg also recognized the C‐terminal peptides of murine, rat, and bovine Plg‐RKT's that contain the same R6K substitution. Plg domains containing disulfide‐bonded kringles (K) inhibited the interaction with the following order of effectiveness: Plg>K1‐3>K5>K4. In conclusion, the interaction of Plg‐RKT with Plg requires the presence of a C‐terminal lysine and can be modulated by a proximal upstream basic residue. Furthermore, kringle domains within the Plg molecule interact with the C‐terminus of Plg‐RKT.