Plasminogen substrate recognition by the streptokinase-plasminogen catalytic complex is facilitated by Arg253, Lys256, and Lys257 in the streptokinase beta-domain and Kringle 5 of the substrate. The Journal of biological chemistry [J Biol Chem] Journal article | | Title | Plasminogen substrate recognition by the streptokinase-plasminogen catalytic complex is facilitated by Arg253, Lys256, and Lys257 in the streptokinase beta-domain and Kringle 5 of the substrate. | | Author(s) | Tharp AC, Laha M, Panizzi P, Thompson MW, Fuentes-Prior P, Bock PE | | Institution | Vanderbilt University School of Medicine, United States; | | Source | J Biol Chem 2009 May 27. | | Abstract | Streptokinase (SK) conformationally activates the central zymogen of the fibrinolytic system, plasminogen (Pg). The SK*Pg* catalytic complex binds Pg as a specific substrate and cleaves it into plasmin (Pm), which binds SK to form the SK*Pm complex that propagates Pm generation. Catalytic complex formation is dependent on lysine-binding site (LBS) interactions between a Pg/Pm kringle and the SK COOH-terminal Lys414. Pg substrate recognition is also LBS-dependent but the kringle and SK structural element(s) responsible have not been identified. SK mutants lacking Lys414 with Ala substitutions of charged residues in the SK beta-domain 250-loop were evaluated in kinetic studies that resolved conformational and proteolytic Pg activation. Activation of [Lys]Pg and mini-Pg (containing only kringle 5 of Pg) by SK with Ala substitutions of Arg253, Lys256, and Lys257 showed decreases in the bimolecular rate constant for Pm generation, with near-total inhibition for the SK Lys256/Lys257 double mutant. Binding of bovine Pg (BPg) to the SK*Pm complex containing fluorescently-labeled Pm demonstrated LBS-dependent assembly of a SK*labeled-Pm*BPg ternary complex, whereas BPg did not bind to the complex containing the SK Lys256/Lys257 mutant. BPg was activated by SK*Pm with a Km indistinguishable from the KD for BPg binding to form the ternary complex, whereas the SK Lys256/Lys257 mutant did not support BPg activation. We conclude that SK residues Arg253, Lys256, and Lys257 mediate Pg substrate recognition through kringle 5 of the [Lys]Pg and mini-Pg substrates. A molecular model of the SK*kringle 5 complex identifies the putative interactions involved in LBS-dependent Pg substrate recognition. | | Language | ENG | | Pub Type(s) | JOURNAL ARTICLE
| | PubMed ID | 19473980 |
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