Clustal W alignment of PYRIN domains, including viral POPs, murine HIN-200 family members p202, p203, p204, and D3, as well as zebrafish caspases. The α-helices, as defined for ASC, are marked on top (H1-6) [205]. Conserved residues are highlighted. Mainly residues of the hydrophobic core are conserved, but the linker distance is variable.