Differential Binding of NLRP3 to non-oxidized and Ox-mtDNA mediates NLRP3 Inflammasome Activation.

The NLRP3 inflammasome is a key mediator of the innate immune response to sterile tissue injury and is involved in many chronic and acute diseases. Physically and chemically diverse agents activate the NLRP3 inflammasome. Here, we show that NLRP3 binds non-oxidized and Ox-mtDNA differentially, with a half maximum inhibitory concentration (IC50) for non-oxidized and Ox-mtDNA of 4 nM and 247.2 nM, respectively. The NLRP3 Neonatal-Onset Multisystem Inflammatory Disease (NOMIDFCAS) gain of function mutant could bind non-oxidized mtDNA but had higher affinity for Ox-mtDNA compared to WT with an IC50 of 8.1 nM. NLRP3 lacking the pyrin domain can bind both oxidized and non-oxidized mtDNA. Isolated pyrin domain prefers Ox-mtDNA. The NLRP3 pyrin domain shares a protein fold with DNA glycosylases and generate a model for DNA binding based on the structure and sequence alignment to Clostridium acetobutylicum and human OGG1, an inhibitor of Ox-mtDNA generation, 8-oxoguanine DNA glycosylases. We provide a new model for how NLRP3 interacts with Ox-mtDNA supported by DNA binding in the presence of a monoclonal antibody against the pyrin domain. These results give new insights into the mechanism of inflammasome assembly, and into the function of reactive oxygen species in establishing a robust immune response.

Small molecule inhibitor binds to NLRP3 and prevents inflammasome activation.

Despite recent advances in the mechanism of oxidized DNA activating NLRP3, the molecular mechanism and consequence of oxidized DNA associating with NLRP3 remains unknown. Cytosolic NLRP3 binds oxidized DNA which has been released from the mitochondria, which subsequently triggers inflammasome activation. Human glycosylase (hOGG1) repairs oxidized DNA damage which inhibits inflammasome activation. The fold of NLRP3 pyrin domain contains amino acids and a protein fold similar to hOGG1. Amino acids that enable hOGG1 to bind and cleave oxidized DNA are conserved in NLRP3. We found NLRP3 could bind and cleave oxidized guanine within mitochondrial DNA. The binding of oxidized DNA to NLRP3 was prevented by small molecule drugs which also inhibit hOGG1. These same drugs also inhibited inflammasome activation. Elucidating this mechanism will enable design of drug memetics that treat inflammasome pathologies, illustrated herein by NLRP3 pyrin domain inhibitors which suppressed interleukin-1ß (IL-1ß) production in macrophages. One-Sentence Summary: NLRP3 cleaves oxidized DNA and small molecule drug binding inhibits inflammasome activation.

Cryo-EM for Small Molecules.

In recent years, protein structure analysis using cryo-electron microscopy(cryo-EM) has expanded and improved. In this review, we discuss many recent improvements to the field, the problems those improvements hope to solve, and some of the still unanswered questions. Most notably, this review will discuss improvements in resolving small or fragmented protein structures, as well as methods to improve the signal-to-noise ratio of the data by increasing image contrast using carbon-based systems. We will also describe how, in the last 5 years, methodological improvements have allowed for better 3D image resolution by capturing a continuum of 3D images. We will provide examples of these methods in practice and discuss how these improved methods may be used in small-molecule drug discovery and development. © 2022 Wiley Periodicals LLC.