Hydration structure of antithrombin conformers and water transfer during reactive loop insertion

Area of Science:

• Biochemistry
• Structural Biology
• Computational Chemistry

Background:

• Antithrombin is a serine protease inhibitor crucial for regulating blood coagulation.
• Functional inhibition involves significant conformational changes, including reactive loop insertion.
• The role of water transfer in these conformational dynamics is not fully understood.

Purpose of the Study:

• To investigate the link between antithrombin's conformational changes and water transfer.
• To quantify water movement during the inhibition of coagulation factor Xa.
• To analyze hydration changes in different antithrombin conformers.

Main Methods:

• X-ray crystallography to determine antithrombin structures.
• Computational geometry (alpha shapes) to analyze hydration fingerprints and water-permeable pockets.
• Osmotic stress assays to measure water transfer rates.

Main Results:

• Distinct hydration fingerprints were observed between loop-exposed and loop-inserted antithrombin conformers.
• Loop-inserted conformers showed a deficit of 61-76 water molecules compared to loop-exposed ones.
• Osmotic stress experiments indicated the transfer of approximately 73 water molecules during inhibition.

Conclusions:

• Conformational changes in antithrombin, particularly reactive loop insertion, are directly associated with water transfer to the bulk solution.
• The study highlights the utility of combining osmotic stress and computational geometry for structure-function analyses.
• This provides new insights into the molecular mechanisms of protease inhibitor function.