Structural factors affecting the choice between latency transition and polymerization in inhibitory serpins

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Plasminogen activator inhibitor-1 (PAI-1) is a serpin protein with unique conformational lability.
• Unlike other serpins that polymerize pathologically, PAI-1 spontaneously converts to a stable, latent form under physiological conditions.

Purpose of the Study:

• To identify specific factors influencing PAI-1's latency conversion.
• To compare PAI-1 mutation effects with alpha(1)-antitrypsin, an archetypal serpin.

Main Methods:

• Site-directed mutagenesis of PAI-1 at various positions.
• Comparison of PAI-1 mutations with equivalent mutations in alpha(1)-antitrypsin.
• Analysis of structural stability and conformational transition rates.

Main Results:

• Mutations near the reactive center loop insertion site (thFs3A, s5A) slowed latency conversion without significantly increasing stability.
• Mutations reducing interactions with beta-sheet C (s2C) facilitated conformational conversion.
• Mutations at Thr93 stabilizing a hydrophobic pocket (s2A) increased structural stability but minimally affected latency transition.

Conclusions:

• PAI-1 latency transition is controlled by highly localized structural features.
• In contrast, other serpins' conformational strain is distributed, leading to polymerization.