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Molecular Characterization and Structural Determination of Nod2, an Innate Immune Receptor

Crohn's disease is a reoccurring inflammatory bowel disease that is proposed to arise from an atypical reaction to commensal bacteria. The human body has designed an intricate system, the innate immune system that specifically deals with the trillions of bacteria that naturally reside within the body. In Crohn's disease, one of the innate immune receptors that senses bacterial cell wall fragments is mutated. The receptor associated with Crohn's disease susceptibility is Nod2. Research suggests that the direct binding of Nod2 and a bacterial cell wall component, muramyl dipeptide (MDP), is responsible for the release of pro‐inflammatory cytokines. However, there is limited understanding of this interaction at the molecular level. By investigating the molecular interactions between Nod2 and MDP, we can determine the mechanism of Crohn's disease. Biochemical assays and structural work utilizing isolated Nod2 have been severely limited by the current low yielding insect and mammalian cell system. A high yielding and active Nod2 construct has been successfully purified from the E.coli system. Using this construct, a variety of different characterization methods have become applicable to probe Nod2 at the molecular level. These include NMR experiments using labeled protein or MDP to map the ligand‐binding pocket of Nod2 and additional mapping of post‐translational modifications using mass spectrometry. Initial crystallographic screenings show promise. Future work aims to elucidate the mechanism of binding between Nod2 and its ligand MDP through co‐crystallization or further in vitro characterization. Funding Acknowledgements: The Pew Charitable Trust and The Chemistry‐Biology Interface (CBI) NIH T32 Training Grant.