Objective—: Inflammation provoked by the imbalance of fatty acid composition, such as excess saturated fatty acids (SFAs), is implicated in the development of metabolic diseases. Recent investigations suggest the possible role of the NLRP3 (nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain containing 3) inflammasome, which regulates IL-1β (interleukin 1β) release and leads to inflammation, in this process. Therefore, we investigated the underlying mechanism by which SFAs trigger NLRP3 inflammasome activation. Approach and Results—: The treatment with SFAs, such as palmitic acid and stearic acid, promoted IL-1β release in murine primary macrophages while treatment with oleic acid inhibited SFA-induced IL-1β release in a dose-dependent manner. Analyses using polarized light microscopy revealed that intracellular crystallization was provoked in SFA-treated macrophages. As well as IL-1β release, the intracellular crystallization and lysosomal dysfunction were inhibited in the presence of oleic acid. These results suggest that SFAs activate NLRP3 inflammasome through intracellular crystallization. Indeed, SFA-derived crystals activated NLRP3 inflammasome and subsequent IL-1β release via lysosomal dysfunction. Excess SFAs also induced crystallization and IL-1β release in vivo. Furthermore, SFA-derived crystals provoked acute inflammation, which was impaired in IL-1β–deficient mice. Conclusions—: These findings demonstrate that excess SFAs cause intracellular crystallization and subsequent lysosomal dysfunction, leading to the activation of the NLRP3 inflammasome, and provide novel insights into the pathogenesis of metabolic diseases.

Significance: Optogenetics is a rapidly growing field in which light is used to control biological systems. We show that Oscillatoria acuminata photoactivated adenylate cyclase (OaPAC) protein produces the fundamental second messenger cyclic-AMP (cAMP) in response to blue light, is stable and functional in different mammalian cell types, and can be used to trigger events by raising cAMP level. OaPAC consists of a catalytic domain controlled by a photosensitive blue light using flavin (BLUF) domain. We have solved the crystal structure to show how activity is triggered by light, and guide mutagenesis experiments. Although the catalytic domain resembles known cyclases, the BLUF domains form an unusual intertwined structure. The protein activity is the same in solution as in the crystal, showing that the activation mechanism involves only small molecular movements.

Despite a large amount of work over the past 30 years, there is still no universal agreement on the differential reactivities of the individual α and β subunits in human hemoglobin. To address this question systematically, we prepared a series of hybrid hemoglobins in which heme was replaced by chromium(III), manganese(III), nickel(II), and magnesium(II) protoporphyrin IXs in either the α or β subunits to produce α₂(M)β₂(Fe)¹and α₂(Fe)β₂(M) tetramers. None of the abnormal metal complexes react with dioxygen or carbon monoxide. The O₂ affinities of the resultant hemoglobins vary from 3 μm ⁻¹ (Cr(III)/Fe(II) hybrids) to 0.003 μm ⁻¹ (Mg(II)/Fe(II) hybrids), covering the full range expected for the various high (R) and low (T) affinity quaternary conformations, respectively, of human hemoglobin A₀. The α and β subunits in hemoglobin have similar O₂ affinities in both quaternary states, despite the fact that the R to T transition causes significantly different structural changes in the α and β heme pockets. This functional equivalence almost certainly evolved to maintain high n values for efficient O₂ transport.