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Ca(2+)-dependent interactions between Gla and EGF domains in human coagulation factor IX
L V Medved1, A Vysotchin, K C Ingham
1J. Holland Laboratory, American Red Cross, Rockville, Maryland 20855.
Biochemistry
|January 18, 1994
Summary
Calcium ions induce a strong interaction between the Gla and EGF domains of human factor IX. This interaction is crucial for factor IX function and can be studied using protein fragments.
Area of Science:
- Biochemistry
- Molecular Biology
- Protein Interactions
Background:
- Human factor IX is a critical protein in the blood coagulation cascade.
- The Gla and EGF domains of factor IX are known to interact, but the nature of this interaction, particularly its calcium dependence, requires further elucidation.
Purpose of the Study:
- To investigate the Ca(2+)-induced interaction between the Gla and EGF domains of human factor IX.
- To characterize the binding properties and structural changes of Gla and EGF domains in the presence and absence of calcium and urea.
Main Methods:
- Size-exclusion chromatography
- Spectroscopic measurements (fluorescence, Tm)
- Use of three protein fragments: 6-kDa Gla, 19-kDa (EGF)2, and 25-kDa Gla-(EGF)2
- Chemical denaturation using 5 M urea
Main Results:
- A stable 1:1 heterocomplex formed between 6-kDa Gla and 19-kDa (EGF)2 fragments in the presence of Ca(2+), indicating a strong Gla-EGF interaction.
- Ca(2+) binding to the 19-kDa (EGF)2 fragment stabilized the first EGF domain, increasing its melting temperature (Tm) by 12°C.
- In 5 M urea, the isolated Gla domain exhibited Ca(2+) binding properties similar to those in the Gla-(EGF)2 fragment, suggesting a compact structure.
Conclusions:
- The Gla and EGF domains of human factor IX exhibit a strong, Ca(2+)-dependent interaction.
- This interaction is essential for the structural integrity and function of factor IX.
- The study provides insights into the molecular mechanisms underlying factor IX activation and regulation.