High molecular weight complex in human plasma between vitamin K-dependent protein S and complement component C4b-binding protein

Proc Natl Acad Sci U S A. 1981 Apr;78(4):2512-6. doi: 10.1073/pnas.78.4.2512.

Abstract

Protein S, a recently described vitamin K-dependent plasma protein, is shown to exist in two forms in plasma--free protein and in complex with C4b-binding protein. C4b-binding protein is involved in the regulation of the rate of complement activation. A major proportion of C4b-binding protein in plasma is in complex with protein S. The complex is a major and previously unrecognized component of the group of plasma proteins that adsorbs to barium citrate. The complex dissociates in the presence of NaDodSO4, indicating that C4b-binding protein and protein S are held together by noncovalent bonds. Uncomplexed C4b-binding protein was purified from the supernatant after barium citrate adsorption. On NaDodSO4/polyacrylamide gels without reduction, it appeared to have a slightly faster migration rate than the C4b-binding protein dissociated from the complex with protein S. After reduction, the subunits of the two forms of C4b-binding protein appeared to have identical molecular weights. Furthermore, there is an equilibrium between free and bound protein S in plasma. The role of protein S in the complex is unknown.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Barium / metabolism
  • Carrier Proteins / metabolism*
  • Complement Inactivator Proteins*
  • Electrophoresis, Polyacrylamide Gel
  • Glycoproteins / metabolism*
  • Humans
  • Macromolecular Substances
  • Molecular Weight
  • Protein Binding
  • Protein S

Substances

  • Carrier Proteins
  • Complement Inactivator Proteins
  • Glycoproteins
  • Macromolecular Substances
  • Protein S
  • Barium