THE STRUCTURE OF THE NON-COVALENT COMPLEX OF RECOMBINANT KRINGLE 1 DOMAIN OF HUMAN PLASMINOGEN WITH EACA (EPSILON-AMINOCAPROIC ACID)
[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 structures of the complexes of the recombinant kringle 1 domain of human plasminogen (Klpg) with the ligands epsilon-aminocaproic acid (EACA) and trans-4-(aminomethyl)cyclohexane-1-carboxylic acid (AMCHA), which are representative of a class of in vivo antifibrinolytic agents, have been determined at 2.1 angstroms resolution. Each Klpg/ligand unit cell contained a dimer of the complexes, and some small differences were noted in the kringle/ligand interatomic distances within the monomeric components of the dimers. The structures obtained allowed predictions to be made of the amino acid residues of Klpg that are likely important to ligand binding. In the crystal structure, the anionic center of Klpg responsible for coordinating the amino group of the ligands is composed of both Asp54 and Asp56, and the cationic center that stabilizes binding of the carboxylate moiety of the ligands is Arg70, with a possible contribution from Arg34. A hydrogen bond between the carboxylate of the ligand to the hydroxyl group of Tyr63 also appears to contribute to the kringle/ligand binding energies. The methylene groups of the ligand are stablized in the binding pocket by van der Waals contacts with side-chain atoms of Trp61 and Tyr71. These conclusions are in general agreement with site-directed mutagenesis results that implicate many of the same amino acid residues in the binding process, thus showing that the crystal and solution structures are in basic accord with each other. Further comparisons of the X-ray crystal structures of the Klpg/ligand complexes with each other and with apo-Klpg show that while small differences in Klpg side-chain geometries may exist in the three structures, the binding pocket can be considered to be preformed in the apokringle and not substantially altered by the nature of the omega-amino acid ligand that is inserted into the site. From the similar geometries of the binding of EACA and AMCHA, it appears that the kon is an important component to the tighter binding of AMCHA to Klpg, as compared to EACA. Ordered solvation effects of the bound AMCHA may contribute to its longer lifetime on Klpg, thereby retarding koff, both effects thus accounting for the higher binding energy of AMCHA as compared to EACA.
Crystal structures of the recombinant kringle 1 domain of human plasminogen in complexes with the ligands epsilon-aminocaproic acid and trans-4-(aminomethyl)cyclohexane-1-carboxylic Acid.,Mathews II, Vanderhoff-Hanaver P, Castellino FJ, Tulinsky A Biochemistry. 1996 Feb 27;35(8):2567-76. PMID:8611560
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.