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Synthesis and characterization of a recombinant hirudin-albumin complex
M D Phaneuf1, R K Ito, F W LoGerfo
1New England Deaconess Hospital/Harvard Medical School, Boston, MA 02215.
Summary
Researchers covalently bound recombinant hirudin (rHir) to albumin, creating a complex that maintains potent alpha-thrombin inhibition. This modification shows promise for new applications of this effective anticoagulant.
Area of Science:
- Biochemistry
- Pharmacology
Background:
- Recombinant hirudin (rHir) is a potent direct inhibitor of alpha-thrombin.
- Albumin is a widely available and biocompatible protein carrier.
Purpose of the Study:
- To covalently conjugate rHir to albumin.
- To evaluate the alpha-thrombin inhibitory activity of the rHir-albumin complex compared to free rHir.
Main Methods:
- Radiolabeling rHir with 125I.
- Covalent conjugation of 125I-rHir to albumin using heterobifunctional cross-linkers.
- Purification of the complex via HPLC and gel filtration chromatography.
- Confirmation of conjugation using SDS-PAGE and autoradiography.
- Enzyme inhibition assays using chromogenic substrate S-2238 to determine inhibition kinetics (Ki values).
Main Results:
- A stable 125I-rHir-albumin complex (average M(r) 78 kDa) was successfully synthesized and purified.
- The complex retained significant protein and radiolabeled hirudin.
- Free 125I-rHir exhibited non-competitive, linear mixed-type inhibition of alpha-thrombin (Ki = 1.61 pM, alpha Ki = 1.09 pM).
- The rHir-albumin complex demonstrated pure non-competitive inhibition (Ki = 15.6 pM), showing a tenfold decrease in potency but retaining significant inhibitory capacity.
Conclusions:
- Covalent binding of rHir to albumin preserves its potent alpha-thrombin inhibitory activity.
- The rHir-albumin conjugate exhibits altered inhibition kinetics but remains a highly effective inhibitor.
- This successful modification provides a basis for developing novel applications for recombinant hirudin as a therapeutic agent.