Asp41-His48 region of streptokinase is important in binding to a substrateplasminogen

Streptokinase is a plasminogen activator protein produced by several strain s of P-hemolytic streptococci. Random mutagenesis of streptokinase was carr ied out for the determination of critical amino acid residues in plasminoge n activation. We selected and sequenced 14 streptokinase mutants with no pl asminogen activation activity on skim milli-plasminogen overlay plate. Spec ific activities of the selected streptokinase mutants were determined with chromogenic assay. Eight mutants (V19F, V35E, E85D, L292R, D325P, D341E, I3 45N, and M369L) resulted in greatly decreased amidolytic activities. Howeve r, unexpectedly, six mutants (D41C, S44K, S44P, R45P, H48T, and D220G) show ed substantial amidolytic activities comparable to that of wild type. Moreo ver, five-point mutations were concentrated on the Asp41-His48 region. Thes e data indicate that the Asp41-His48 region in a streptokinase-plasminogen binary complex plays an important role in binding to a substrate plasminoge n. (C) 2000 Elsevier Science Ltd. All rights reserved.