Membrane Cofactor Protein: Importance of<i>N</i>- and<i>O</i>-Glycosylation for Complement Regulatory Function

Liszewski, M. Kathryn; Leung, Marilyn K.; Atkinson, John P.

doi:10.4049/jimmunol.161.7.3711

Cited by 45 publications

(1 citation statement)

References 49 publications

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“…N‐terminal His 6 ‐tagged DAF CCP2–4 (residues 97–285) and MCP CCP1–4 (residues 35–285), as glycosylated alternative to the E. coli product, were purified from medium after expression in HEK293. Purified MCP (CCP1–4) from both E. coli and HEK293 showed comparable activity (Fig EV1), confirming previous observations that glycosylation at the three potential glycosylation sites does not affect cofactor activity (Liszewski et al , ). Full‐length β2‐glycoprotein I (β2GPI) and its fragment CCP1–4 were recombinantly expressed in HEK293 cells.…”

Section: Methodssupporting

confidence: 89%

Regulators of complement activity mediate inhibitory mechanisms through a common C3b‐binding mode

et al. 2016

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Regulators of complement activation (RCA) inhibit complement‐induced immune responses on healthy host tissues. We present crystal structures of human RCA (MCP, DAF, and CR1) and a smallpox virus homolog (SPICE) bound to complement component C3b. Our structural data reveal that up to four consecutive homologous CCP domains (i–iv), responsible for inhibition, bind in the same orientation and extended arrangement at a shared binding platform on C3b. Large sequence variations in CCP domains explain the diverse C3b‐binding patterns, with limited or no contribution of some individual domains, while all regulators show extensive contacts with C3b for the domains at the third site. A variation of ~100° rotation around the longitudinal axis is observed for domains binding at the fourth site on C3b, without affecting the overall binding mode. The data suggest a common evolutionary origin for both inhibitory mechanisms, called decay acceleration and cofactor activity, with variable C3b binding through domains at sites ii, iii, and iv, and provide a framework for understanding RCA disease‐related mutations and immune evasion.

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Section: Methodssupporting

confidence: 89%

Regulators of complement activity mediate inhibitory mechanisms through a common C3b‐binding mode

et al. 2016

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Control of C3b and C5b deposition by CD46 (membrane cofactor protein) after alternative but not classical complement activation

et al. 1999

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C3b and C5b deposition following complement activation, and its regulation by CD46 were studied using xenogenic Chinese hamster ovary (CHO) cells as targets and cytofluorometry. Following activation of the alternative pathway, an initial low level of C3b deposition was observed on CHO cell surfaces after a lag time of approximately 4 min. This was followed by a secondary high level of C3b deposition with a slower rate. C3b deposition was maximal within 15 min. When CD46 was expressed (B2 isoform), the kinetics of C3b deposition were essentially unchanged, but the onset of the secondary high C3b deposition was fully prevented. C5b deposition was also observed on CHO but not on CHO.CD46 cells following activation of the alternative pathway. Activation of the classical pathway on CHO and CHO.CD46 cells, using factor B-depleted human serum and anti-CHO antibodies, resulted in almost identical single-peak C3b deposition profiles. Accordingly, no regulation of C5b deposition by CD46 was evident following activation of the classical pathway. These data indicate that CD46 prevents the C3b deposition amplification loop mediated by the alternative C3 convertase and, consequently, inhibits the formation of the alternative C5 convertase. But CD46 prevents neither the spontaneous tick-over C3b deposition leading to the formation of the alternative C3 convertase nor the formation of the functional classical C3 and C5 convertases.

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Analysis of genes coding for CD46, CD55, and C4b‐binding protein in patients with idiopathic, recurrent, spontaneous pregnancy loss

et al. 2013

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Summary Since a tightly regulated complement system is needed for a successful pregnancy, we hypothesized that alterations in complement inhibitors may be associated with idiopathic, recurrent miscarriage. We sequenced all exons coding for three complement inhibitors: C4b-binding protein (C4BP), CD46 and CD55 in 384 childless women with at least two miscarriages that could not be explained by known risk factors. Several alterations were found in C4BPA, of which the R120H, I126T, and the G423T mutations affected the expression level and/or the ability of recombinant C4BP to serve as cofactor for factor I. The only variant in C4BPB was located in the C-terminal part, and did not impair the polymerization of the molecule. Our results identify for the first time alterations in C4BP in women experiencing recurrent miscarriages. We also found four CD46 alterations in individual patients that were not found in healthy controls. One of the rare variants, P324L, showed decreased expression, whereas N213I resulted in deficient protein processing as well as an impaired cofactor activity in the degradation of both C4b and C3b. The identified alterations may result in in vivo consequences and contribute to the disorder but the degree of association must be evaluated in larger cohorts.

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Membrane Cofactor Protein: Importance ofN- andO-Glycosylation for Complement Regulatory Function

Cited by 45 publications

References 49 publications

Regulators of complement activity mediate inhibitory mechanisms through a common C3b‐binding mode

Regulators of complement activity mediate inhibitory mechanisms through a common C3b‐binding mode

Control of C3b and C5b deposition by CD46 (membrane cofactor protein) after alternative but not classical complement activation

Analysis of genes coding for CD46, CD55, and C4b‐binding protein in patients with idiopathic, recurrent, spontaneous pregnancy loss

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