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High molecular weight complex in human plasma between vitamin K-dependent protein S and complement component
Summary
Protein S, a vitamin K-dependent protein, exists freely or bound to C4b-binding protein in plasma. This complex, crucial for complement regulation, is held by noncovalent bonds and dissociates in NaDodSO4.
Area of Science:
- Biochemistry
- Immunology
- Hematology
Background:
- Protein S is a vitamin K-dependent plasma protein.
- C4b-binding protein regulates complement activation.
- A significant portion of C4b-binding protein circulates complexed with Protein S.
Purpose of the Study:
- To investigate the forms of Protein S in plasma.
- To characterize the complex between Protein S and C4b-binding protein.
- To understand the nature of the interaction between these proteins.
Main Methods:
- Plasma protein analysis using NaDodSO4/polyacrylamide gel electrophoresis.
- Barium citrate adsorption to isolate protein complexes.
- Purification of uncomplexed C4b-binding protein.
Main Results:
- Protein S exists in both free and C4b-binding protein-bound forms in plasma.
- The Protein S-C4b-binding protein complex is a significant plasma component.
- The complex dissociates in NaDodSO4, indicating noncovalent interactions.
- Subtle differences in C4b-binding protein migration were observed, but subunits were identical after reduction.
Conclusions:
- Protein S and C4b-binding protein form a dissociable complex in plasma.
- Noncovalent bonds mediate the interaction between Protein S and C4b-binding protein.
- The functional role of Protein S within this complex remains to be elucidated.