PubMed · 13756680
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P KLEIN. 1960. [On specific blocking of 4 complement components by anticomplement].. https://pubmed.ncbi.nlm.nih.gov/13756680/
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A variable endogenous retroviral element has been identified in intron 9 of the complement C4 gene [HERV-K(C4)], which maps to the class III region of the major histocompatibility complex (MHC) on chromosome 6p21.3. Genetic susceptibility to type I diabetes is mainly conferred by the MHC locus and the complement C4 region has been implied to contribute to human leukocyte antigen DQ (HLA-DQ) mediated disease risk. As the HERV-K(C4) insertion has been suggested to modulate expression of homologous genes, we investigated its transmission in 220 families with an offspring affected by type I diabetes as a potential disease susceptibility marker. There was no preferential transmission of the HERV-K(C4) insertion to affected offspring (P(TDT) = 0.79). Although 77.7% of HLA-DQ8 carried the HERV-K(C4) insertion, only 52.9% of -DQ2 haplotypes did (P(chi(2)) < 0.01). However, its insertion or deletion did not modulate the risk conferred by HLA-DQ8 (DQA1*0301-DQB1*0302) (P(chi(2)) = 0.27) or -DQ2 (DQA1*0501-DQB1*0201) (P(chi(2)) = 0.46). Thus, the HERV-K(C4) insertion is not associated with type I diabetes in Germans.
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Complex formation between the human complement proteins C4b and C2 was investigated by surface plasmon resonance. C4b was immobilised and C2 was used in the fluid phase to measure interaction at different ionic strengths (30-830 mM NaCl) and in the absence and presence of MgCl2. Maximum binding was observed at 30 mM NaCl, and was negligible above 300 mM NaCl. Binding was not greatly influenced by variation in Mg(2+) in the range of 2.5-15 mM. C4bC2 affinity (Kd) was determined by steady-state analysis to be 7.2x10(-8) M in physiological conditions (10 mM Hepes, 2.5 mM MgCl2, 0.75 mM CaCl2 and 140 mM NaCl, pH 7.4). For C4(H2O)C2 complex formation, a Kd of 4.0x10(-8) M was calculated. As far as detected by the applied method, complex formation does not involve conformational changes of one of the binding partners. Consistent with previous reports, C4bC2 binding takes place as a multiple-site binding event in the presence of Mg2+. C4bC2 complex formation in 10 mM Hepes, 2.5 mM EDTA and 140 mM NaCl (pH 7.4) was also observed and the interaction showed characteristics of a single-site binding event. Kd was 1.5x10(-8) M. Complement factor B (FB) was also tested for its binding to immobilised C4b. Weak interaction was observed at FB concentrations in the physiological range (500-1000 nM). Kd was 1.2x10(-6) M, indicating possible cross-reactivity between classical and alternative pathways of the activation of the complement system.