Polymerization of plasminogen activator inhibitor-1

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Chemistry

Background:

• Plasminogen activator inhibitor-1 (PAI-1) is a serine proteinase inhibitor (serpin) that regulates its activity via intramolecular loop incorporation.
• Other serpins can form pathological polymers through intermolecular linkage, a trait not previously observed in active PAI-1.

Purpose of the Study:

• To investigate whether PAI-1, unlike other active serpins, can form polymers.
• To characterize the polymerization process and properties of PAI-1 polymers.

Main Methods:

• Recombinant native and latent PAI-1 were subjected to low pH conditions in vitro.
• Electrophoretic analysis was used to detect and differentiate polymerization patterns.
• Dissociation of formed polymers was assessed.

Main Results:

• Both native and latent PAI-1 spontaneously form polymers in vitro at low pH, exhibiting distinct electrophoretic patterns.
• Unlike polymers of other serpins, PAI-1 polymers readily dissociate back to their monomeric form.
• Polymerization mechanisms involve beta-strand addition of the reactive loop to different beta-sheets (s7A in native PAI-1, s1C in latent PAI-1).
• Glycosylated PAI-1 also forms polymers under similar conditions.

Conclusions:

• PAI-1 is not unique among active serpins and can form polymers, challenging previous assumptions.
• PAI-1 polymerization is reversible, suggesting distinct linkage mechanisms compared to other serpins.
• The formation of PAI-1 polymers in low pH environments, such as platelets, may have in vivo relevance.