HpBoRB, a helminth-derived CCP domain protein which binds RELMβ.

Helminth infections persist by influencing host immunity through the release of immunomodulatory proteins which prevent immune ejection. The intestinal nematode Heligmosomoides polygyrus bakeri (Hpb) secretes multiple families of immunomodulatory proteins, many of which are composed of consecutive Complement Control Protein (CCP) domains. We hypothesised that further CCP domain proteins are secreted by the parasite to interact with the host. We identified an unusually large number of CCP domain-containing proteins in the genome of Hpb, and cloned a range of these for screening in an Avidity-based Extracellular Interaction Screening (AVEXIS) assay, focussing on interactions with host immune proteins. This screen confirmed the binding of known immunomodulators (HpBARI, TGM1) for their targets (ST2, TGFBR2) and identified a new interaction between a 2 CCP domain Hpb protein and mouse resistin-like molecule beta (RELMβ), a host protein demonstrated to have anti-helminth properties. This protein was named Binder of RELMβ (HpBoRB). This interaction was specific and heat-labile, and was confirmed in ELISA, competition assays, size exclusion chromatography and surface plasmon resonance experiments, identifying a subnanomolar affinity interaction between HpBoRB and RELMβ. These data may indicate that Hpb interferes with the potent anti-helminth host protein RELMβ and adds to our knowledge of the host-parasite interactions mediated by Hpb secreted proteins.