Characterization of Lys-698-to-Met substitution in human plasminogen catalytic domain

Proteins. 2004 Aug 1;56(2):277-84. doi: 10.1002/prot.20070.


Streptokinase (SK) is a human plasminogen (Pg) activator secreted by streptococci. The activation mechanism of SK differs from that of physiological Pg activators in that SK is not a protease and cannot proteolytically activate Pg. Instead, it forms a tight complex with Pg that proteolytically activates other Pg molecules. The residue Lys-698 of human Pg was hypothesized to participate in triggering activation in the SK-Pg complex. Here, we report a study of the Lys-698 to Met substitution in the catalytic domain of Pg (microPg) containing the proteolytic activation-resistant background (R561A). While it remains competent in forming a complex with SK, maintaining a comparable equilibration dissociation constant (K(D)), the recombinant protein shows a nearly 60-fold reduction in amidolytic activity relative to its R561A background when mixed with native SK. A 2.3 A crystal structure of this mutant microPg confirmed the correct folding of this recombinant protein. Combined with other biochemical data, these results support the premise that Lys-698 of human Pg plays a functional role in the so-called N-terminal insertion activation mechanism by SK.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Substitution
  • Binding Sites
  • Catalysis
  • Chromogenic Compounds / metabolism
  • Crystallography, X-Ray
  • Enzyme Activation / drug effects
  • Humans
  • Lysine / chemistry
  • Macromolecular Substances
  • Methionine / chemistry
  • Models, Molecular
  • Molecular Sequence Data
  • Mutation, Missense
  • Plasminogen / chemistry*
  • Plasminogen / metabolism
  • Pliability
  • Protein Binding
  • Protein Conformation
  • Protein Folding
  • Protein Interaction Mapping
  • Protein Structure, Tertiary
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism
  • Streptokinase / metabolism
  • Streptokinase / pharmacology
  • Structure-Activity Relationship
  • Surface Plasmon Resonance


  • Chromogenic Compounds
  • Macromolecular Substances
  • Recombinant Fusion Proteins
  • Plasminogen
  • Methionine
  • Streptokinase
  • Lysine

Associated data

  • PDB/1RJX