Hagelueken, G. | bioRxiv Science

bioRxiv2021

Cryo-EM structure of the NLRP3 decamer bound to the cytokine release inhibitory drug CRID3

NLRP3 is an intracellular sensor protein whose activation by a broad spectrum of exogenous and endogenous stimuli leads to inflammasome formation and pyroptosis. The mechanisms leading to NLRP3 activation and the way how antagonistic small molecules function remain poorly understood. Here we report the cryo-electron microscopy structures of full-length NLRP3 in its native form and complexed with the inhibitor CRID3 (also named MCC950). Inactive, ADP-bound NLRP3 is a decamer composed of homodimers of intertwined LRR domains that assemble back-to-back as pentamers with the NACHT domain located at the apical axis of this spherical structure. Molecular contacts between the concave sites of two opposing LRRs are mediated by an acidic loop extending from an LRR transition segment. Binding of CRID3 significantly stabilizes the NACHT and LRR domains relative to each other, allowing structural resolution of 3.9-4.2 [A]. CRID3 binds into a cleft, connecting four subdomains of the NACHT with the transition LRR. Its central sulfonylurea group interacts with the Walker A motif of the NLRP3 nucleotide-binding domain and is sandwiched between two arginines from opposing sites, explaining the specificity of NLRP3 for this chemical entity. With the determination of the binding site of this lead therapeutic, specific targeting of NLRP3 for the treatment of autoinflammatory and autoimmune diseases and rational drug optimization are within reach.

immunology↗

bioRxiv2020

Triggering closure of a sialic acid TRAP transporter substrate binding protein through binding of natural or artificial substrates

The pathogens Vibrio cholerae and Haemophilus influenzae use tripartite ATP-independent periplasmic transporters (TRAPs) to scavenge sialic acid from host tissues. They use it as a nutrient or to evade the innate immune system by sialylating surface lipopolysaccharides. An essential component of TRAP transporters is a periplasmic substrate binding protein (SBP). Without substrate, the SBP has been proposed to rest in an open-state, which is not recognised by the transporter. Substrate binding induces a conformational change of the SBP and it is thought that this closed state is recognised by the transporter, triggering substrate translocation. Here we use real time single molecule FRET experiments and crystallography to investigate the open- to closed-state transition of VcSiaP, the SBP of the sialic acid TRAP transporter from V. cholerae. We show that the conformational switching of VcSiaP is strictly substrate induced, confirming an important aspect of the proposed transport mechanism. Two new crystal structures of VcSiaP provide insights into the closing mechanism. While the first structure contains the natural ligand, sialic acid, the second structure contains an artificial peptide in the sialic acid binding site. Together, the two structures suggest that the ligand itself stabilises the closed state and that SBP closure is triggered by physically bridging the gap between the two lobes of the SBP. Finally, we demonstrate that the affinity for the artificial peptide substrate can be substantially increased by varying its amino acid sequence and by this, serve as a starting point for the development of peptide-based inhibitors of TRAP transporters.

biophysics↗