Structure and function of human tissue-type plasminogen activator (t-PA)

Area of Science:

• Molecular Biology
• Biochemistry
• Protein Engineering

Background:

• Tissue-type plasminogen activator (t-PA) is crucial for fibrinolysis.
• Understanding t-PA domain function is key to developing targeted therapies.
• Previous studies suggested domain-specific roles, but precise mapping was needed.

Purpose of the Study:

• To delineate functional domains within the heavy (H)-chain of t-PA.
• To identify regions responsible for fibrin-mediated activity enhancement.
• To confirm the location of the catalytic domain and PAI interaction site.

Main Methods:

• Construction of t-PA deletion mutants using cDNA.
• Transient expression of recombinant mutant proteins in mouse Ltk- cells.
• Assays to evaluate enzymatic activity, substrate specificity, fibrin stimulation, and PAI binding.

Main Results:

• The serine protease activity and plasminogen specificity reside solely in the light (L)-chain.
• Fibrin-mediated stimulation of t-PA activity is primarily mediated by the K2 domain and secondarily by the finger domain.
• The K1 and epidermal growth factor-like domains of the H-chain do not contribute to fibrin stimulation.
• The primary binding site for plasminogen activator inhibitor (PAI) is located within the L-chain.

Conclusions:

• The H-chain domains, particularly K2 and finger, are critical for fibrin-dependent activation of t-PA.
• The L-chain harbors the essential catalytic machinery and the main PAI interaction site.
• These findings provide a detailed map of t-PA functional domains, aiding in the design of improved thrombolytic agents.