Distinct axial and lateral interactions within homologous filaments dictate the signaling specificity and order of the AIM2-ASC inflammasome.

Inflammasomes are filamentous signaling platforms integral to innate immunity. Currently, little is known about how these structurally similar filaments recognize and distinguish one another. A cryo-EM structure of the AIM2PYD filament reveals that the architecture of the upstream filament is essentially identical to that of the adaptor ASCPYD filament. In silico simulations using Rosetta and molecular dynamics followed by biochemical and cellular experiments consistently demonstrate that individual filaments assemble bidirectionally. By contrast, the recognition between AIM2 and ASC requires at least one to be oligomeric and occurs in a head-to-tail manner. Using in silico mutagenesis as a guide, we also identify specific axial and lateral interfaces that dictate the recognition and distinction between AIM2 and ASC filaments. Together, the results here provide a robust framework for delineating the signaling specificity and order of inflammasomes.

Bilayer compositional asymmetry influences the nanoscopic to macroscopic phase domain size transition.

The eukaryotic plasma membrane (PM) exhibits lipid mixing heterogeneities known as lipid rafts. These lipid rafts, the result of liquid-liquid phase separation, can be modeled by coexisting liquid ordered (Lo) and liquid disordered (Ld) domains. Four-lipid component systems with a high-melting lipid, a nanodomain-inducing low-melting lipid, a macrodomain-inducing low-melting lipid, and cholesterol (chol) can give rise to domains of different sizes. These four-component systems have been characterized in experiments, yet there are few studies that model the asymmetric distribution of lipids actually found in the PM. We used molecular dynamics (MD) simulations to analyze the transition from nanoscopic to macroscopic domains in symmetric and in asymmetric model membranes. Using coarse-grained MD simulations, we found that asymmetry promotes macroscopic domain growth in a case where symmetric systems exhibit nanoscopic domains. Also, macroscopic domain formation in symmetric systems is highly dependent on registration of like phases in the cytoplasmic and exoplasmic leaflets. Using united-atom MD simulations, we found that symmetric Lo domains are only slightly more ordered than asymmetric Lo domains. We also found that large Lo domains in our asymmetric systems induce a slight chain ordering in the apposed cytoplasmic regions. The chol fractions of phase-separated Lo and Ld domains of the exoplasmic leaflet were unchanged whether the system was symmetric or asymmetric.