Roles of the Picornaviral 3C Proteinase in the Viral Life Cycle and Host Cells

Sun, Di; Chen, Shun; Cheng, Anchun; Wang, Mingshu

The host intrinsic immune defense against invading pathogens is closely related to the activation of parallel pattern recognition receptor (PRR) pathways that facilitate the production of type I interferon (IFN). PRRs detect conserved molecular signatures of pathogens, termed pathogen-associated molecular patterns (PAMPs), to distinguish host components from pathogens [90] . Vertebrate hosts encode several classes of PRRs, such as RIG-I-like receptors (RLRs), NOD-like receptors, C-type lectin receptors and Toll-like receptors (TLRs) [91, 92] . Two well-known pattern recognition receptors are Toll-like receptors (PPRs) and RIG-I-like RNA helicases (RLHs). Notably, all TLRs are type I transmembrane proteins composed of a leucine-rich N-terminal of an ectodomain, a transmembrane domain, and a linker to a cytoplasmic C-terminal Toll-interleukin-I receptor (TIR) homology domain [93, 94] . The RLR family, comprising RIG-I, MDA5 and LGP2, has a conserved DExD/H-box helicase domain and a C-terminal domain (CTD).