The notion that animals can detect the Earth's magnetic field was once ridiculed, but is now well established. Yet the biological nature of such magnetosensing phenomenon remains unknown. Here, we report a putative magnetic receptor (Drosophila CG8198, here named MagR) and a multimeric magnetosensing rod-like protein complex, identified by theoretical postulation and genome-wide screening, and validated with cellular, biochemical, structural and biophysical methods. The magnetosensing complex consists of the identified putative magnetoreceptor and known magnetoreception-related photoreceptor cryptochromes (Cry), has the attributes of both Cry- and iron-based systems, and exhibits spontaneous alignment in magnetic fields, including that of the Earth. Such a protein complex may form the basis of magnetoreception in animals, and may lead to applications across multiple fields.

NOD-like receptors (NLRs) localize in the cytosol to recognize intracellular pathogen products and initialize the innate immune response. However, the ligands and ligand specificity of many NLRs remain unclear. One such NLR, NLRP6, plays an important role in maintaining intestinal homeostasis and protecting against various intestinal diseases such as colitis and intestinal tumorigenesis. Here, we show that the major component of the outer membrane of gram-negative bacteria, lipopolysaccharide (LPS), binds NLRP6 directly and induces global conformational change and dimerization. Following stimulation by ATP, the NLRP6 homodimer can further assemble into a linear molecular platform, and ASC is recruited to form higher molecular structures, indicative of a step-by-step activation mechanism. Our study sheds light on the mystery of LPS-induced inflammasome initiation, reveals the architecture and structural basis of potential pre-inflammasome, and suggests a novel molecular assembly pattern for immune receptors. The innate immune system is essential in the first line of defense against microbial infection, tissue injury and regulating the adaptive immune system. The initiation of innate immune responses relies on the recognition of conserved structures or products of pathogens by pattern recognition receptors (PRRs). Toll-like receptors (TLRs) and newly identified nod-like receptors (NLRs) are key PRRs in the innate immune system. TLRs recognize a wide variety of microbial products outside the cell or in intracellular endosomes and lysosomes and NLRs localize in cytosol to detect intracellular pathogen products 1. Twenty-two NLRs have been identified in humans and all share typical tripartite domain architecture: the N-terminal domain recruits downstream effector molecules by homotypic protein-protein interactions; the central nucleotide-binding oligomerization (NOD, or NACHT) domain enables activation of the signaling complex via nucleotide-dependent oligomerization; and the C-terminal leucine-rich repeat (LRR) domain recognizes microbial ligands in a manner analogous to TLRs. Studies on NOD1, NOD2, NLRP1, NLRP3, NLRX1 and NLRC4 suggest a direct interaction between NLRs and cytoplasmic pathogen-and damage-associated molecules 2-9 , however, ligands and ligand specificity remain poorly understood for the majority of NLRs. Following ligand binding and activation, intracellular NLRs assemble into multimeric molecular platforms such as inflammasomes and trigger innate immune defenses 6,10. Our knowledge of inflammasomes is mainly derived from studies of NLRP1, NLRP3 and NLRC4, whereby these NLRs form inflammasomes with the adaptor ASC and Caspase-1, promoting the maturation of the inflammatory cytokines IL-1b and IL-18 6,10,11. NLRP6 (Fig. 1a) is one of 14 pyrin domain-containing members of the NLR family and participates in inflammasome assembly 12-16. A major focus of the last decade has been detailing the immune response and signaling pathway