Function of streptokinase fragments in plasminogen activation

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Chemistry

Background:

• Streptokinase (SK) is a bacterial protein used to activate human plasminogen (hPlg) for thrombolytic therapy.
• Understanding the structure-function relationship of SK peptide fragments is crucial for developing more effective therapeutic agents.

Purpose of the Study:

• To identify and characterize functional peptide fragments of streptokinase (SK).
• To elucidate the roles of specific SK fragments in human plasmin (hPlm) binding and human plasminogen (hPlg) activation.

Main Methods:

• Incubation of streptokinase with immobilized human plasmin.
• Purification of peptide fragments using high-performance liquid chromatography (HPLC).
• Determination of N-terminal sequences, amino acid compositions, and molecular masses.

Main Results:

• A 36 kDa fragment (SK-p, Ser60-Lys387) showed high affinity for hPlm and retained significant hPlg activation ability.
• A 30 kDa fragment (SK-o, Ser60-Lys333) exhibited minimal hPlg activator activity and low hPlm affinity.
• The N-terminal 7 kDa fragment (SK-m, Ile1-Lys59) enhanced the activity of other fragments but had no intrinsic activator function.
• A 18 kDa fragment (SK-n, Glu148-Lys333) showed no activator activity.

Conclusions:

• The Ser60-Lys333 region (SK-o) is essential for minimal streptokinase activator function.
• The C-terminal Ala334-Lys387 peptide within SK-p is critical for high-affinity binding to human plasmin.
• The N-terminal 59 amino acids (SK-m) are important for maintaining streptokinase's proper conformation and full activator potency.