THE STRUCTURE OF RECOMBINANT PLASMINOGEN KRINGLE 1 AND THE FIBRIN BINDING SITE
[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 structure of recombinant (Hoover et al. Biochemistry, 1993; 32:10936-10944) plasminogen (PG) kringle 1 (K1) has been determined and refined at 2.48 A resolution to a crystallographic R value of 0.159. In addition, 71 water molecules and two chloride ions have been located. The folding of PGK1 is very similar to that of PGK4. The lysine/fibrin binding site, however, differs from that of both PGK4 and tissue-type PG activator (t-PA) K2 at the cationic centre. Although PGK1 can potentially have a doubly charged cationic centre utilizing Arg34 and Arg71, the side chain of Arg34 is outside of Arg71 in a solvent region and its guanidino group is flexibly disordered. Moreover, site specific mutagenesis studies show unequivocally that Arg34 can be changed to glutamine without affecting the binding ability of PGK1. Thus, PGK1 only has Arg71 at the cationic site, PGK4 has Lys35/Arg71 and t-PAK2 has only Lys33. The cationic site differences may result in subtle responses in the binding affinities of the kringles. The two chloride ions are located in the lysine binding site and effectively compensate the positive charges of the region. They also appear to be involved intermolecularly in a complex way in the crystal structure. Such intermolecular anionic interactions are also found in PGK4 and t-PAK2.
The structure of recombinant plasminogen kringle 1 and the fibrin binding site.,Wu TP, Padmanabhan KP, Tulinsky A Blood Coagul Fibrinolysis. 1994 Apr;5(2):157-66. PMID:8054447
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.