Proteolytic Processing of Nlrp1b Is Required for Inflammasome Activity

Nlrp1b is a NOD-like receptor that detects the catalytic activity of anthrax lethal toxin and subsequently co-oligomerizes into a pro-caspase-1 activation platform known as an inflammasome. Nlrp1b has two domains that promote oligomerization: a NACHT domain, which is a member of the AAA+ ATPase family, and a poorly characterized Function to Find Domain (FIIND). Here we demonstrate that proteolytic processing within the FIIND generates N-terminal and C-terminal cleavage products of Nlrp1b that remain associated in both the auto-inhibited state and in the activated state after cells have been treated with lethal toxin. Functional significance of cleavage was suggested by the finding that mutations that block processing of Nlrp1b also prevent the ability of Nlrp1b to activate pro-caspase-1. By using an uncleaved mutant of Nlrp1b, we established the importance of cleavage by inserting a heterologous TEV protease site into the FIIND and demonstrating that TEV protease processed this site and induced inflammasome activity. Proteolysis of Nlrp1b was shown to be required for the assembly of a functional inflammasome: a mutation within the FIIND that abolished cleavage had no effect on self-association of a FIIND-CARD fragment, but did reduce the recruitment of pro-caspase-1. Our work indicates that a post-translational modification enables Nlrp1b to function

Electronic state and local surrounding of 119Sn in calcium-substituted holmium orthochromites

The influence of Ca2+ doped into the holmium sublattice on the magnetically active surrounding of Sn4+ ions located in the chromium sublattice of Ho1–xCaxCr0.997Sn0.003O3 (x = 0, 0.003, and 0.1) compounds was studied by 119Sn Mössbauer spectroscopy. At concentrations [Ca] = [Sn] = 0.3 mol %, an increase was observed in the spectral contribution of Sn4+ sites, having the full number of nearest-neighbor Cr3+cations (n = 6), where they perceived a magnetic field H(Sn)4.2 K = 82 kOe, compared to the contribution of the relevant sites in the undoped chromite (x = 0). This observation was interpreted as resulting from a reduced probability of appearance of Cr3+ vacancies in the nearest surrounding of heterovalent Sn4+ ions. For x = 0.1, on the contrary, the 119Sn spectrum revealed a reduced contribution from the Sn4+ sites with n = 6. This evolution is shown not to be due neither to the appearance of Cr4+ nor Cr6+ ions in the nearest neighborhood of Sn4+ in the chromium sublattice to balance the charge deficiency of the Ca2+ ions doped into the holmium sublattice. This allowed us to suggest that the observed effect was due to the onset of Sn4+ segregations in the structure of Ho0.9Ca0.1Cr0.997Sn0.003O3, which contained a far greater amount of Ca2+ ions whose charge deficiency was balanced mostly by Cr4+ formation. Studies of samples that were prepared under a hydrogen atmosphere revealed the reduction of Sn4+ to the oxidation state +2, with the concomitant stabilization of the formed Sn2+ ions on crystallite surfaces on sites having low coordination numbers