Summary
Plasminogen activator inhibitor type 1 (PAI-1) is a central regulator of fibrinolysis
and tissue remodelling. PAI-1 belongs to the serpin super-family and unlike other
inhibitory serpins undergoes a spontaneous inactivation process under physiological
conditions, termed latency transition. During latency transition the solvent exposed
reactive centre loop is inserted into the central β–sheet A of the molecule, and is
no longer accessible to reaction with the protease. More than three decades of research
on mammalian PAI-1 has not been able to clarify the evolutionary advantage and physiological
relevance of latency transition. In order to study the origin of PAI-1 latency transition,
we produced PAI-1 from Spiny dogfish shark (Squalus acanthias) and African lungfish (Protopterus sp.), which represent central species in the evolution of vertebrates. Although human
PAI-1 and the non-mammalian PAI-1 variants share only approximately 50 % sequence
identity, our results showed that all tested PAI–1 variants undergo latency transition
with a similar rate. Since the functional stability of PAI–1 can be greatly increased
by substitution of few amino acid residues, we conclude that the ability to undergo
latency transition must have been a specific selection criterion for the evolution
of PAI-1. It appears that all PAI-1 molecules must harbour latency transition to fulfil
their physiological function, stressing the importance to further pursue a complete
understanding of this molecular phenomenon with possible implication to pharmacological
intervention. Our results provide the next step in understanding how the complete
role of this important protease inhibitor evolved along with the fibrinolytic system.
Supplementary Material to this article is available online at www.thrombosis-online.com.
Keywords
Conformational change - thermodynamic stability - urokinase - tissue type plasminogen
activator - homology