IDENTIFICATION OF THE FUNCTIONAL IMPORTANCE OF VALINE-19 RESIDUE IN STREPTOKINASE BY N-TERMINAL DELETION AND SITE-DIRECTED MUTAGENESIS

Streptokinase (SK) is a bacterial plasminogen activator of multi-domai n structure. In deletion analysis of the N-terminal region of SK, the deletion of 20 amino acids (SK Delta N20) resulted in the dramatic red uction of plasminogen activator activity compared to deletion of 7 (SK Delta N7) and 13 amino acids (SK Delta N13). The incubation time to r each maximal active site generation in an equimolar mixture of SK Delt a N20 and plasminogen was the same as that for wild-type SK. To identi fy the functional residues important in plasminogen activation, severa l site-directed mutations were introduced at the region spanning Ser16 -Val20 of SK. The results showed that Val19 residue is important for t he activity of the SK-plasminogen complex.