The carbohydrate-linked phosphorylcholine of the parasitic nematode product ES-62 modulates complement activation

Umul Kulthum Ahmed, N. Claire Maller, Asif J. Iqbal, Lamyaa Al-Riyami, William Harnett, John G. Raynes

Research output: Contribution to journalArticle

10 Citations (Scopus)
47 Downloads (Pure)

Abstract

Parasitic nematodes manufacture various carbohydratelinked phosphorylcholine (PCh)-containing molecules, including ES-62, a protein with an N-linked glycan terminally substituted with PCh. The PCh component is biologically important because it is required for immunomodulatory effects. We showed that most ES-62 was bound to a single protein, C-reactive protein (CRP), in normal human serum, displaying a calcium-dependent, high-avidity interaction and ability to form large complexes. Unexpectedly, CRP binding to ES-62 failed to efficiently activate complement as far as the C3 convertase stage in comparison with PCh-BSA and PCh-containing Streptococcus pneumoniae cell wall polysaccharide. C1q capture assays demonstrated an ES-62-CRP-C1q interaction in serum. The three ligands all activated C1 and generated C4b to similar extents. However, a C2a active site was not generated following ES-62 binding to CRP, demonstrating that C2 cleavage was far less efficient for ES-62-containing complexes. We proposed that failure of C2 cleavage was due to the flexible nature of carbohydrate-bound PCh and that reduced proximity of the C1 complex was the reason that C2 was poorly cleaved. This was confirmed using synthetic analogues that were similar to ES-62 only in respect of having a flexible PCh. Furthermore, ES-62 was shown to deplete early complement components, such as the rate-limiting C4, following CRP interaction and thereby inhibit classical pathway activation. Thus, flexible PCh-glycan represents a novel mechanism for subversion of complement activation. These data illustrate the importance of the rate-limiting C4/C2 stage of complement activation and reveal a new addition to the repertoire of ES-62 immunomodulatory mechanisms with possible therapeutic applications.

Original languageEnglish
Pages (from-to)11939-11953
Number of pages15
JournalJournal of Biological Chemistry
Volume291
Issue number22
Early online date4 Apr 2016
DOIs
Publication statusPublished - 27 May 2016

Keywords

  • parasitic nematode manufacture
  • human parasites
  • inflammatory diseases

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