Prothrombinase processivity is conferred by substrate allostery

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• The prothrombinase complex (factor Xa and factor Va) is crucial for blood coagulation.
• Understanding its mechanism of prothrombin conversion to thrombin is vital.
• Structural insights into substrate binding are lacking.

Purpose of the Study:

• To elucidate the molecular basis of prothrombin processing by the prothrombinase complex.
• To provide structural insights into substrate and intermediate binding.
• To reveal the enzymatic mechanism of thrombin generation.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine structures.
• Structures of prothrombinase bound to prothrombin and meizothrombin were solved at 3.1 Å resolution.

Main Results:

• A surprising interaction was found between factor Va heavy chain and prothrombin exosite I.
• Cleavage at Arg320 induces significant conformational changes in meizothrombin.
• These changes rearrange the substrate to expose the second cleavage site.

Conclusions:

• The prothrombinase complex employs a unique mechanism involving substrate participation.
• A new paradigm of 'substrate allostery' is introduced.
• This mechanism explains the rapid and processive conversion of prothrombin to thrombin.