Refined structure of the hirudin-thrombin complex

Area of Science:

• Biochemistry and structural biology
• Protein-protein interactions
• Enzyme inhibition

Background:

• Thrombin is a key enzyme in blood coagulation.
• Hirudin is a potent natural inhibitor of thrombin.
• Understanding their complex structure is crucial for drug development.

Purpose of the Study:

• To determine the high-resolution structure of the recombinant hirudin-thrombin complex.
• To elucidate the molecular interactions responsible for thrombin inhibition by hirudin.

Main Methods:

• X-ray crystallography
• Restrained least-squares refinement
• Structural analysis

Main Results:

• The hirudin N-terminal domain binds to the thrombin active site, interacting with the catalytic triad.
• Hirudin forms a parallel beta-strand with thrombin, differing from other serine proteinase inhibitors.
• The C-terminal segment of hirudin interacts with the fibrinogen binding exosite via electrostatic and hydrophobic interactions.
• High affinity and specificity result from numerous, collectively strong interactions.

Conclusions:

• The precise complementarity between hirudin and thrombin underlies their strong binding.
• Structural differences in the autolysis loop are likely due to crystal packing.
• The RGD sequence in thrombin may not mediate surface interactions in this complex.