KRINGLE 2 DOMAIN OF HUMAN PLASMINOGEN: NMR SOLUTION STRUCTURE OF TRANS-4-AMINOMETHYLCYCLOHEXANE-1-CARBOXYLIC ACID (AMCHA) COMPLEX
[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 kringle 2 (K2) module of human plasminogen (Pgn) binds L-lysine and analogous zwitterionic compounds, such as the antifibronolytic agent trans-(aminomethyl)cyclohexanecarboxylic acid (AMCHA). Far-UV CD and NMR spectra reveal little conformational change in K2 upon ligand binding. However, retarded (1)H-(2)H isotope exchange kinetics induced by AMCHA indicate stabilization of the K2 conformation by the ligand. Assessment of secondary structure content from CD spectra yields approximately 26% beta-STRAND, approximately 13% beta-TURN, approximately 15% 3(1)-HELIX, and approximately 6% 3(10)-HELIX. The NMR solution conformation of the K2 domain complexed to AMCHA has been determined [heavy atom rmsd = 0.49 +/- 0.09A (BACKBONE) AND 1.02+/- 0.08 (ALL)]. The K2 molecule has overall dimensions of approximately 34.5A times approximately 33.4A times approximately 22.7A . Analogous with the polypeptide outline of homologous domains, K2 contains three short antiparallel beta-sheets (paired strands 15-16/20-21, 24-25/48-49, and 62-64/72-74) and four defined beta-turns (residues 6-9, 16-19, 53-56, AND 67-70). Consistent with the CD analysis, albeit novel in the context of kringle folding, the NMR structure reveals an unpaired beta-strand structured by residues 30-32, a turn of 3(10)-helix compromising residues 38-41, and a 3(1)-helix for residues 21-24 and 74-79. We also identify alignable 3(1)-helices in previously reported homologous kringle structures. Rather high order parameter S(2) values (<S(2)>= approximately 0.85 +/- 0.04) characterize the K2 backbone dynamics. The lowest flexibility is observed for the two inner loop segments of residues 51-63 AND 63-75 (<S(2)>= approximately 0.86-0.87 +/- 0.03). Overhauser connectivities reveal close hydrophobic contacts of the ligand ring with side chains of Tyr(36), Trp(62), Phe(64), Trp(72), AND Leu(74). In most K2 structures, the N atom of AMCHA places itself approximately 3.9 and 4.4A from the anionic groups of Glu(57) and Asp(55), respectively, while its carboxylate group, H-bonded to the Tyr(36) side chain OH(eta), ion-pairs the Arg(71) guanidinium group. Consistent with the preference of K2 for binding 5-aminopentanoic acid over 6-aminohexanoic acid, the positions of the ionic centers within the K2 binding site approach each other approximately 1A closer relative to what is observed in lysine binding sites of homologous Pgn modules.
Solution structure and dynamics of the plasminogen kringle 2-AMCHA complex: 3(1)-helix in homologous domains.,Marti DN, Schaller J, Llinas M Biochemistry. 1999 Nov 30;38(48):15741-55. PMID:10625440
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.