The structure of endosomal ArfGEF BRAG2 in complex with Arf1, combined with an analysis of this GEF's efficiency on membranes, reveals a regulatory mechanism that simultaneously optimizes membrane recruitment and nucleotide exchange.

Interleukin (IL) 11 activates multiple intracellular signaling pathways by forming a complex with its cell surface α-receptor, IL-11Rα, and the β-subunit receptor, gp130. Dysregulated IL-11 signaling has been implicated in several diseases, including some cancers and fibrosis. Mutations in IL-11Rα that reduce signaling are also associated with hereditary cranial malformations. Here we present the first crystal structure of the extracellular domains of human IL-11Rα and a structure of human IL-11 that reveals previously unresolved detail. Disease-associated mutations in IL-11Rα are generally distal to putative ligand-binding sites. Molecular dynamics simulations showed that specific mutations destabilize IL-11Rα and may have indirect effects on the cytokine-binding region. We show that IL-11 and IL-11Rα form a 1:1 complex with nanomolar affinity and present a model of the complex. Our results suggest that the thermodynamic and structural mechanisms of complex formation between IL-11 and IL-11Rα differ substantially from those previously reported for similar cytokines. This work reveals key determinants of the engagement of IL-11 by IL-11Rα that may be exploited in the development of strategies to modulate formation of the IL-11–IL-11Rα complex.

The great benefits that chemical pesticides have brought to agriculture are partly offset by widespread environmental damage to nontarget species and threats to human health. Microbial bioinsecticides are considered safe and highly specific alternatives but generally lack potency. Spindles produced by insect poxviruses are crystals of the fusolin protein that considerably boost not only the virulence of these viruses but also, in cofeeding experiments, the insecticidal activity of unrelated pathogens. However, the mechanisms by which spindles assemble into ultra-stable crystals and enhance virulence are unknown. Here we describe the structure of viral spindles determined by X-ray microcrystallography from in vivo crystals purified from infected insects. We found that a C-terminal molecular arm of fusolin mediates the assembly of a globular domain, which has the hallmarks of lytic polysaccharide monooxygenases of chitinovorous bacteria. Explaining their unique stability, a 3D network of disulfide bonds between fusolin dimers covalently crosslinks the entire crystalline matrix of spindles. However, upon ingestion by a new host, removal of the molecular arm abolishes this stabilizing network leading to the dissolution of spindles. The released monooxygenase domain is then free to disrupt the chitinrich peritrophic matrix that protects insects against oral infections. The mode of action revealed here may guide the design of potent spindles as synergetic additives to bioinsecticides.ost entomopoxviruses (EV) produce two types of intracellular crystals. Virus-containing spheroids are the main infectious form of EV (1) and are functionally analogous to polyhedra of cypovirus (2) and baculovirus (3, 4). In contrast, the function of the second type of crystals is less clear. These crystals of the viral fusolin protein, called "spindles" because of their characteristic shape, assemble in the endoplasmic reticulum of infected cells and for some species also occur embedded within the crystalline lattice of spheroids (5). Purified spindles are not infectious but strongly enhance the infectivity of EV by a mechanism that involves disruption of the peritrophic matrix, a physical barrier that protects the midgut epithelium of insects against oral pathogens (6, 7). Remarkably, in larval cofeeding experiments, spindles also enhance the insecticidal activity of unrelated oral pathogens such as baculovirus (8) and the Bacillus thuringiensis (Bt) toxin (9) by up to three orders of magnitude. This effect on virulence prompted their use as synergistic additives to common bioinsecticides, for instance by transgenic expression of spindles in plants to improve the effectiveness of baculovirus insecticides (10).Fusolin proteins have a signal sequence that targets them to the endoplasmic reticulum, and the mature protein has a mass of 36-44 kDa. Some fusolins are glycosylated, and the glycosylation site of the fusolin produced by Anomala cuprea EV (ACEV) is required for full virulence (11). Sequence analysis shows that the N-terminal regio...

Gastrointestinal epithelial cells provide a selective barrier that segregates the host immune system from luminal microorganisms, thereby contributing directly to the regulation of homeostasis. We have shown that from early embryonic development Bcl-G, a Bcl-2 protein family member with unknown function, was highly expressed in gastrointestinal epithelial cells. While Bcl-G was dispensable for normal growth and development in mice, the loss of Bcl-G resulted in accelerated progression of colitisassociated cancer. A label-free quantitative proteomics approach revealed that Bcl-G may contribute to the stability of a mucin network, which when disrupted, is linked to colon tumorigenesis. Consistent with this, we observed a significant reduction in Bcl-G expression in human colorectal tumors. Our study identifies an unappreciated role for Bcl-G in colon cancer.