Molecular evolution of plasminogen activator inhibitor-1 functional stability

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Engineering

Background:

• Plasminogen activator inhibitor-1 (PAI-1) is a crucial regulator of blood coagulation within the serine protease inhibitor (serpin) family.
• PAI-1 exhibits unique active and latent conformations, with the active form being transient and its structure unknown.
• Understanding PAI-1's conformational dynamics is key to its role in hemostasis and thrombosis.

Purpose of the Study:

• To investigate the structural basis for PAI-1's conformational instability.
• To engineer recombinant PAI-1 variants with enhanced functional stability.
• To elucidate the role of specific mutations in PAI-1's stability and function.

Main Methods:

• Construction of a randomly mutated recombinant PAI-1 expression library.
• Screening of the library using bacteriophage display for increased functional stability.
• Functional half-life (T1/2) assays to quantify the stability of selected PAI-1 variants.

Main Results:

• Fourteen unique PAI-1 variants with functional half-lives up to 72-fold greater than wild-type were identified.
• The most stable variant, with a T1/2 of 145 hours, required the synergistic contribution of four specific mutations.
• Individual mutations showed limited impact, highlighting the importance of multi-site interactions for enhanced stability.

Conclusions:

• The identified mutations suggest that PAI-1's active conformation instability arises from global protein packing changes.
• Engineered PAI-1 variants demonstrate the potential for stabilizing this critical regulator.
• The transient nature of PAI-1's active form may confer a selective evolutionary advantage for inhibitor function.