Will the discovery of cross-α amyloid-like fibrils herald a new definition of amyloid?

In microorganisms, functional amyloid is often involved in virulence mechanisms. Staphylococcus aureus secretes a 22-residue phenol-soluble modulin α3 (PSMα3) peptide, capable of forming elongated fibrils, with the appearance and staining properties typical of amyloid. Researchers working to solve the 3D structure of PSMα3 fibrils by X-ray crystallography were in for a surprise. As reported by Tayeb-Fligelman et al in their recent publication in Science, fibrils of PSMα3 revealed a distinctive “cross-α” amyloid-like architecture instead of the classical cross-β spine, hitherto considered the hallmark of amyloid.