Biochemical mechanisms of inflammasome function

点击翻译按钮获取中文摘要

The innate immune system acts as the first line of defense for animals and plants in reconciling cellular injury and infection through the early detection of impending threats, and consequential triggering of pro-inflammatory responses. The NOD-like receptors-containing pyrin (NLRP) subfamily of proteins have emerged as key sensors of intracellular danger signals. Rapidly developing biological models now indicate the various NLRPs are of paramount importance in initiating inflammatory responses to cellular injury; however, critical aspects regarding the underlying biochemistry of this protein family and their signaling complexes remain unresolved. NLRPs contain a central NACHT domain with ATP-binding and hydrolysis properties, (sometimes referred to as the nucleotide-binding oligomerization domain or NOD) that designate NLRPs as members of the larger ATPases-Associated with various cellular Activities (AAA+ ATPase) superfamily. The enzymatic properties of NACHT domains are thought to regulate NLRP oligomerization and inflammasome activation, yet much remains to be understood regarding its structure and function. NLRP3 is the most thoroughly studied and is considered to be the prototypical inflammasome-forming member, yet the basic biochemistry of NLRP3 as well as the remaining NLRP proteins (14 members in the family) remains incompletely characterized. Many assumptions regarding the enzymatic activity of NLRPs and the intrinsic regulation of inflammasome formation are based primarily upon analogy with limited corroborating evidence. Further characterization of the enzymology of inflammasome activation as well as the integration of recently revealed post-translational modifications in regulating inflammatory signaling pathways will be critical for a comprehensive understanding of this protein family. In this regard, we propose that specific biochemical properties of different NLRPs drive distinctions in catalytic activities, which in turn can impact upon oligomerization and inflammatory signaling. Thus, a definition of the enzymology of NLRP proteins and the role of ATP in driving inflammasome assembly and activation of downstream signaling pathways will be important to advance understanding of this innate immune process. It is clear that holistic studies of the entire NLRP family are necessary, and we will creatively advance understanding of the NLRP family as a whole and their propensity to assemble into functional inflammasomes. To address the knowledge deficit, systems for the effective production of all NLRP proteins will be defined, biochemical assessments of enzymatic function will be completed, novel technologies and reagents for biological interrogations will be developed, and precise structural definitions of the catalytic NACHT domain will be generated. Our technical advances in recombinant NLRP protein production support biochemical analyses of inflammasome catalytic function as well as structural biology approaches.