Necroptosis is an immunogenic form of programmed cell death that is dependent on the kinase RIPK3 and independent of caspase-8. Necroptosis has been implicated in multiple disease states, including inflammatory bowel disease and ischaemic injury after stroke, so there is significant interest in the development of necroptosis modulators and diagnostics. A functional amyloid complex referred to as the necrosome is central to necroptosis. The protein RIPK3 comprises the majority of the necrosome, which forms via intermolecular interactions involving an ~18 residue sequence motif called a Receptor interacting protein (RIP) Homotypic Interaction Motif (RHIM). The RHIM drives the folding of RIPK3 into the characteristic amyloid cross-ß structure, which recruits additional monomers to generate highly stable, insoluble amyloid fibrils.
There are currently no small molecules available that selectively bind to the amyloidogenic RHIM region of RIPK3. Here, the RIPK3 RHIM region has been used as the target for the cyclic peptide screening technology termed random non-standard peptide integrated discovery (RaPID). The RHIM-containing region was subject to selection from a cyclic peptide library, both in the process of assembling from monomers into oligomeric and fibrillar forms, as well as in a performed fibrillar form. From this library, several novel cyclic peptides were identified, and therefore have the potential to bind specifically to the RIPK3 RHIM amyloid interface. These peptides may have the potential for use in the specific modulation of necroptosis, and as diagnostic tools to detect RIPK3 functional amyloid formation.