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Analysis of the interactions between streptokinase domains and human plasminogen
Author(s) -
ConejeroLara Francisco,
Parrad Juan,
Azuaga Ana I.,
Dobson Christopher M.,
Ponting Chris P.
Publication year - 1998
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.5560071017
Subject(s) - benzamidine , chemistry , surface plasmon resonance , lysine , stereochemistry , binding site , biophysics , dissociation constant , cleavage (geology) , streptokinase , plasma protein binding , plasmin , covalent bond , biochemistry , amino acid , enzyme , biology , receptor , paleontology , materials science , fracture (geology) , nanoparticle , nanotechnology , psychology , organic chemistry , psychiatry , myocardial infarction
The contrasting roles of streptokinase (SK) domains in binding human Glu l‐plasminogen (Plg) have been studied using a set of proteolytic fragments, each of which encompasses one or more of SK's three structural domains (A, B, C). Direct binding experiments have been performed using gel filtration chromatography and surface plasmon resonance. The latter technique has allowed estimation of association and dissociation rate constants for interactions between Plg and intact SK or SK fragments. Each of the SK fragments that contains domain B (fragments A2‐B‐C, A2‐B, B‐C, and B) binds Plg with similar affinity, at a level approximately 100‐ to 1,000‐fold lower than intact SK. Experiments using 10 mM 6‐aminohexanoic acid or 50 mM benzamidine demonstrate that either of these two lysine analogues abolishes interaction of domain B with Plg. Isolated domain C does not show detectable binding to Plg. Moreover, the additional presence of domain C within other SK fragments (B‐C and A2‐B‐C) does not alter significantly their affinities for Plg. In addition, Plg‐binding by a noncovalent complex of two SK fragments that contains domains A and B is similar to that of domain B. By contrast, species containing domain B and both domains A and C (intact SK and the two‐chain complex A1·A2‐B‐C) show a significantly higher affinity for Plg, which could not be completely inhibited by saturating amounts of 6‐AHA. These results show that SK domain B interacts with Plg in a lysine‐dependent manner and that although domains A and C do not appear independently to possess affinity for Plg, they function cooperatively to establish the additional interactions with Plg to form an efficient native‐like Plg activator complex.