Characterization of NLRP3 inflammasome components in the endangered Chinese giant salamander (Andrias davidianus)

Chinese giant salamander (Andrias davidianus) is the largest extant urodela species and has unique evolutionary position. Studying the immune system of Chinese giant salamander contributes to understanding the evolution of immune systems of vertebrates. The NLR-related protein 3 (NLRP3) inflammasome comprised of NLRP3, ASC and caspase-1 play important roles in the host innate immunity. However, little is know about the NLRP3 inflammasome components in Chinese giant salamander. In this study, the NLRP3, apoptosis-associated speck-like protein (ASC) and caspase-1 (adaNLRP3, adaASC and adaCaspase-1) were characterized from Chinese giant salamander. The proteins of these three genes shared similar motifs and structures with their mammalian counterparts, with a PYD motif, a nucleotide-binding domain (NACHT) motif, and four leucine-rich repeat domain (LRR) motifs identified in adaNLRP3, a pyrin domain (PYD) motif and a caspase recruitment domain (CARD) motif in adaASC, and a CARD motif and a CASc motif in adaCaspase-1. These three genes were constitutively expressed in the skin, heart, lung, kidney, muscle, brain, spleen, and liver of Chinese giant salamander. Following Aeromonas hydrophia infection, all the three genes were up-regulated in various tissues. Molecular docking analysis revealed that the key residues involved in forming the adaNLRP3/adaASC complex were located in the PYD motifs, and that involved in forming the adaASC/adaCaspase-1 complex were located in the CARD motifs. Further analysis revealed that the hydrogen bonds and salt bridges had crucial roles in the formation of adaNLRP3/acaASC and adaASC/adaCaspase-1 complexes. To the best of our knowledge, this is the first report on the NLRP3 inflammasome components in Chinese giant salamander which will be helpful in further understanding the function of the NLRP3 inflammasome and in elucidating its role in the immune response to microbes.