STRUCTURE AND LIGAND DETERMINANTS OF THE RECOMBINANT KRINGLE 5 DOMAIN OF HUMAN PLASMINOGEN
[PLMN_HUMAN] Defects in PLG are the cause of plasminogen deficiency (PLGD) [MIM:217090]. PLGD is characterized by decreased serum plasminogen activity. Two forms of the disorder are distinguished: type 1 deficiency is additionally characterized by decreased plasminogen antigen levels and clinical symptoms, whereas type 2 deficiency, also known as dysplasminogenemia, is characterized by normal, or slightly reduced antigen levels, and absence of clinical manifestations. Plasminogen deficiency type 1 results in markedly impaired extracellular fibrinolysis and chronic mucosal pseudomembranous lesions due to subepithelial fibrin deposition and inflammation. The most common clinical manifestation of type 1 deficiency is ligneous conjunctivitis in which pseudomembranes formation on the palpebral surfaces of the eye progresses to white, yellow-white, or red thick masses with a wood-like consistency that replace the normal mucosa.       
[PLMN_HUMAN] Plasmin dissolves the fibrin of blood clots and acts as a proteolytic factor in a variety of other processes including embryonic development, tissue remodeling, tumor invasion, and inflammation. In ovulation, weakens the walls of the Graafian follicle. It activates the urokinase-type plasminogen activator, collagenases and several complement zymogens, such as C1 and C5. Cleavage of fibronectin and laminin leads to cell detachment and apoptosis. Also cleaves fibrin, thrombospondin and von Willebrand factor. Its role in tissue remodeling and tumor invasion may be modulated by CSPG4. Binds to cells. Angiostatin is an angiogenesis inhibitor that blocks neovascularization and growth of experimental primary and metastatic tumors in vivo.
Publication Abstract from PubMed
The X-ray crystal structure of the recombinant (r) kringle 5 domain of human plasminogen (K5HPg) has been solved by molecular replacement methods using K1HPg as a model and refined at 1.7 A resolution to an R factor of 16.6%. The asymmetric unit of K5HPg is composed of two molecules related by a noncrystallographic 2-fold rotation axis approximately parallel to the z-direction. The lysine binding site (LBS) is defined by the regions His33-Thr37, Pro54-Val58, Pro61-Tyr64, and Leu71-Tyr74 and is occupied in the apo-form by water molecules. A unique feature of the LBS of apo-K5HPg is the substitution by Leu71 for the basic amino acid, arginine, that in other kringle polypeptides forms the donor cationic center for the carboxylate group of omega-amino acid ligands. While wild-type (wt) r-K5HPg interacted weakly with these types of ligands, replacement by site-directed mutagenesis of Leu71 by arginine led to substantially increased affinity of the ligands for the LBS of K5HPg. As a result, binding of omega-amino acids to this mutant kringle (r-K5HPg[L71R]) was restored to levels displayed by the companion much stronger affinity HPg kringles, K1HPg and K4HPg. Correspondingly, alkylamine binding to r-K5HPg[L71R] was considerably attenuated from that shown by wtr-K5HPg. Thus, employing a rational design strategy based on the crystal structure of K5HPg, successful remodeling of the LBS has been accomplished, and has resulted in the conversion of a weak ligand binding kringle to one that possesses an affinity for omega-amino acids that is similar to K1HPg and K4HPg.
Structure and ligand binding determinants of the recombinant kringle 5 domain of human plasminogen.,Chang Y, Mochalkin I, McCance SG, Cheng B, Tulinsky A, Castellino FJ Biochemistry. 1998 Mar 10;37(10):3258-71. PMID:9521645
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.