Abstract
Innate immune signaling is mediated by a number of membrane-anchored or cytosolic receptor or sensor molecules. Several receptor families utilize conserved signaling domains such as the Toll/interleukin-1 receptor (TIR) domain and Pyrin domain (PYD) to link microbe recognition to induction of proinflammatory cytokines and interferons. Recent studies have identified a number of bacterial and viral TIR domains and PYD domains that directly target the signaling function of their host homologues. Emerging biochemical and structural studies of these microbial TIR and PYD domains suggest that they are mimics of their host counterparts at the sequence and structure levels. Unraveling the mechanisms of such molecular mimicry is crucial to our understanding and clinical intervention of infectious diseases and inflammatory disorders.