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Dobó J, Gál P, Szilágyi K, Cseh S, Lörincz Z, Schumaker VN, Závodszky P. One Active C1r Subunit Is Sufficient for the Activity of the Complement C1 Complex: Stabilization of C1r in the Zymogen Form by Point Mutations. THE JOURNAL OF IMMUNOLOGY 1999. [DOI: 10.4049/jimmunol.162.2.1108] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Abstract
The binding of C1 (the first component of complement) to immune complexes leads to the autoactivation of C1r through the cleavage of the Arg463-Ile464 bond in the catalytic domain. Spontaneous activation of C1r (and C1) also occurs in the fluid phase, preventing the characterization of the zymogen form of C1r. To overcome this difficulty, the zymogen form of human C1r was stabilized by mutating the Arg in the Arg463-Ile464 bond to Gln. This mutant was designated as mutant QI. Recombinant C1r (wild type (wt) or mutant) was expressed in insect cells using serum-free medium in functionally pure form; therefore, the cell culture supernatant was suitable to reconstruct C1 for the hemolytic assay. Mutant QI was a stable, nonactivable zymogen and showed no hemolytic activity in reconstituted C1. However, this stable zymogen C1r mutant could form an active mixed dimer with the wt C1r, indicating that one active C1r subunit in the C1 complex is sufficient for the full activity of the entire complex. Our experiments also showed that the exchange of C1r monomers between the C1r dimers is completed in less than 16 h even at pH 7 and 4°C. Two other mutants were also constructed by changing Arg463 to Lys, or Ile464 to Phe, and were designated as mutants KI and RF, respectively. Although these substitutions did increase the stability of the proenzyme in the cell culture supernatant, the mutant proteins retained their ability to autoactivate, and both had a wt-like hemolytic activity.
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Affiliation(s)
- József Dobó
- *Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest, Hungary; and
| | - Péter Gál
- *Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest, Hungary; and
| | - Katalin Szilágyi
- *Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest, Hungary; and
| | - Sándor Cseh
- *Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest, Hungary; and
| | - Zsolt Lörincz
- *Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest, Hungary; and
| | - Verne N. Schumaker
- †Molecular Biology Institute, and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095
| | - Péter Závodszky
- *Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest, Hungary; and
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Falus A, Füst G, Erdei A. Complement research: biosynthesis, genetics, immunoregulatory role and clinical studies. IMMUNOLOGY TODAY 1992; 13:A10-2. [PMID: 1510803 DOI: 10.1016/0167-5699(92)90057-e] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Complementology is one of the major areas of immunological research in Hungary. Here, András Falus and colleagues describe studies on the control of biosynthesis of complement components and on the nature and function of receptors in the complement system.
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Affiliation(s)
- A Falus
- Dept of Molecular Biology, National Institute of Rheumatology, Budapest, Hungary
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Baumann MA, Anderson BE. An immune complex selective affinity matrix utilizing a synthetic peptide. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(17)44768-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Flamini G, Ria F, Pizzigallo E, Gignina S. Chromatographic and electrophoretic studies of immune complexes in non-A, non-B hepatitis. JOURNAL OF CHROMATOGRAPHY 1988; 426:55-64. [PMID: 3133383 DOI: 10.1016/s0378-4347(00)81926-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Immune complexes isolated from two patients with chronic non-A, non-B hepatitis, one patient with acute non-A, non-B hepatitis and one patient with juvenile rheumatoid arthritis were examined by means of a combined chromatographic and electrophoretic method. Both analyses showed the presence of complexes consisting of IgG, IgM, complement c1q factor and albumin; no antigen constituents were detected. The IgG-to-IgM ratio varied from 1:1 to 4:1, suggesting that one could be dealing with complexes of both IgG-IgM and IgG-IgG types. Moreover, the detectable presence of c1q factor might indicate that such complexes were capable of activating complement.
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Affiliation(s)
- G Flamini
- Institute of General Pathology, Catholic University, Rome, Italy
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Abstract
Interactions between C1q and other subunits of C1 were analyzed by sucrose gradient ultracentrifugation. A zone of dilute, radioiodine labelled C1q was sedimented through uniform concentrations of either C1r2C1s2, C1r2, C1r2 or C1s(2). The dissociation constants were found to be 3 x 10(-9) M and 6 x 10(-9) M for C1r2C1s2 and C1r2 binding respectively. Hill coefficients of 1 indicated no cooperativity in these bindings. Positive cooperativity was found in binding of C1s to C1q. Dissociation constants of 2 x 10(-6) M and 5 x 10(-8) M were obtained form computer modelling of a two step binding mechanism. No interaction was detected between C1q and activated C1r2. The data indicate that most of the interactions between C1q and C1r2C1s2 originates from a strong binding to the C1r2 moiety of the zymogen complex. This interaction is lost upon activation of C1r2.
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Affiliation(s)
- S Lakatos
- Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest
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