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Related Experiment Videos

Human C4-binding protein. I. Isolation and characterization.

J Scharfstein, A Ferreira, I Gigli

    The Journal of Experimental Medicine
    |July 1, 1978
    PubMed
    Summary
    This summary is machine-generated.

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    C4-binding protein (C4-bp), a complement system component, was purified from human plasma. This glycoprotein binds C4b, forming complexes that can affect electrophoretic patterns in serum.

    Area of Science:

    • Immunology
    • Biochemistry

    Background:

    • The complement system is crucial for innate and adaptive immunity.
    • C4-binding protein (C4-bp) is a newly identified component of this system.
    • Understanding C4-bp's properties is essential for its role in immune responses.

    Purpose of the Study:

    • To isolate and characterize C4-binding protein (C4-bp) from human plasma.
    • To investigate the binding interaction between C4-bp and C4b.
    • To determine the molecular properties and behavior of C4-bp and its complexes.

    Main Methods:

    • Isolation of C4-bp via polyethyleneglycol precipitation and ion-exchange chromatography.
    • Identification using SDS-PAGE, C4b-binding assays, and immunoprecipitation.
    • Characterization of C4-bp and C4b/C4-bp complexes using ultracentrifugation and crossed immunoelectrophoresis (CIE).

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    Main Results:

    • Purified C4-bp is a 10.7 s glycoprotein composed of disulfide-bonded subunits (70 kDa), with a total molecular weight of 540-590 kDa.
    • C4-bp binds to C4b, forming stable complexes (15-17 s) independent of divalent cations.
    • C4-bp demonstrated multivalency, with saturation occurring at C4b/C4-bp ratios of 4-5.

    Conclusions:

    • C4-bp is a distinct complement protein that binds C4b.
    • The interaction between C4-bp and C4b can influence electrophoretic analyses of complement proteins in serum.
    • Stable C4-bp and C4 complexes are not formed in EDTA-plasma, allowing for separate identification.