Resolving distinct molecular origins for copper effects on PAI-1

Area of Science:

• Biochemistry
• Molecular Biology
• Hemostasis

Background:

• The fibrinolytic system requires tight regulation for hemostasis.
• Plasminogen activator inhibitor-1 (PAI-1) is a critical serpin regulating fibrinolysis.
• Active PAI-1 is unstable and prone to latent conversion, influenced by ligands like vitronectin.

Purpose of the Study:

• To investigate the molecular mechanisms of copper's effect on PAI-1 stability.
• To characterize the role of N-terminal histidine residues in copper binding and PAI-1 latency.
• To understand how copper influences PAI-1 stability in the presence or absence of vitronectin.

Main Methods:

• Development of a gel-based copper sensitivity assay for PAI-1.
• Comparison of wild-type PAI-1 with variants lacking specific histidine residues.
• Kinetic and thermodynamic analysis of copper binding using isothermal titration calorimetry.

Main Results:

• Identified a copper-binding site involving histidines at positions 2 and 3, significantly stabilizing PAI-1.
• Observed differential copper sensitivity in PAI-1 variants, correlating with histidine presence.
• Discovered a second, independent metal-binding site that accelerates PAI-1 latency conversion.

Conclusions:

• N-terminal histidines mediate a novel copper-binding interaction that stabilizes PAI-1.
• Copper binding significantly enhances PAI-1 stability, exceeding that conferred by vitronectin alone.
• These findings elucidate a new regulatory mechanism for PAI-1 and its role in hemostasis.