Structure of a bacterial Rhs effector exported by the type VI secretion system

The type VI secretion system (T6SS) is a widespread protein export apparatus found in Gram-negative bacteria. The majority of T6SSs deliver toxic effector proteins into competitor bacteria. Yet, the structure, function, and activation of many of these effectors remains poorly understood. Here, we present the structures of the T6SS effector RhsA from Pseudomonas protegens and its cognate T6SS spike protein, VgrG1, at 3.3 Å resolution. The structures reveal that the rearrangement hotspot (Rhs) repeats of RhsA assemble into a closed anticlockwise β-barrel spiral similar to that found in bacterial insecticidal Tc toxins and in metazoan teneurin proteins. We find that the C-terminal toxin domain of RhsA is autoproteolytically cleaved but remains inside the Rhs ‘cocoon’ where, with the exception of three ordered structural elements, most of the toxin is disordered. The N-terminal ‘plug’ domain is unique to T6SS Rhs proteins and resembles a champagne cork that seals the Rhs cocoon at one end while also mediating interactions with VgrG1. Interestingly, this domain is also autoproteolytically cleaved inside the cocoon but remains associated with it. We propose that mechanical force is required to remove the cleaved part of the plug, resulting in the release of the toxin domain as it is delivered into a susceptible bacterial cell by the T6SS.     

Isolation and characterization of nine microsatellite markers from Coffea arabica L., showing wide cross‐species amplifications

Genetic improvement of coffee (Coffea arabica L.) is constrained by low genetic diversity and lack of genetic markers, suitable screening tools, information on the genetic make‐up of available gene pool and long generation time. In this context, use of DNA markers such as microsatellites that provide high genetic‐resolution becomes highly desirable. Here, we report the development of nine new microsatellite markers from partial genomic library of an elite variety of Coffea arabica. The developed microsatellites revealed robust cross‐species amplifications in 17 related species of coffee, and their Polymorphic Information Content varied from 0 to 0.6, 0 to 0.78 and 0.67 to 0.90 for the arabica, robusta genotypes and species representatives, respectively. The data thus suggest their potential use as genetic markers for assessment of germplasm diversity and linkage analysis of coffee.     

Role of lysosome rupture in controlling Nlrp3 signaling and necrotic cell death

The Nod-like receptor, Nlrp3, has been linked to inflammatory diseases and adjuvant-mediated immune responses. A wide array of structurally diverse agents does not interact directly with Nlrp3, but is thought to activate the Nlrp3 inflammasome by inducing a common upstream signal, such as lysosome rupture. To test the connection between lysosome integrity and Nlrp3 signaling, we analyzed inflammasome activation following stimulation of murine macrophages with lysosome-destabilizing agents and pyroptosis inducers. Here we provide evidence that lysosomal rupture and the corresponding release of lysosomal hydrolases is an early event in macrophages exposed to the lysosome-destabilizing adjuvants LLOMe and alum. Lysosome rupture preceded cell death induction mediated by these agents and was associated with the degradation of low-molecular weight proteins, including the inflammasome component caspase-1. Proteolysis of caspase-1 was controlled by specific cathepsins, but was independent of autocatalytic processes and Nlrp3 signaling. Consistent with these findings, lysosome-disrupting agents triggered only minimal caspase-1 activation and failed to cause caspase-1-dependent cell death (pyroptosis), generally associated with Nlrp3 signaling. In contrast, lysosome rupture was a late event in macrophages exposed to prototypical pyroptosis inducers. These agents triggered extensive Nlrp3 signaling prior to lysosome rupture with only minimal impact on the cellular proteome. Taken together, our findings suggest that lysosome impairment triggers a cascade of events culminating in cell death but is not crucial for Nlrp3 signaling. The significant differences observed between lysosome-disrupting agents and pyroptosis inducers might explain the distinct immunologic responses associated with these compounds.     

Hyperinsulinemia and ectopic fat deposition can develop in the face of hyperadiponectinemia in young obese rats

Serum adiponectin has been reported to inversely correlate with the degree of adiposity in children. However, the relative contribution of adiponectin-dependent signaling to the development of metabolic syndrome in childhood obesity is unclear. We overfed prepubertal, male Sprague-Dawley rats a high-fat diet via total enteral nutrition. Excessive caloric intake led to obesity, increased body weight and fat mass; dyslipidemia; ectopic fat deposition; and hyperinsulinemia (P<.05). Expression of fatty acid transporter FAT/CD36 was elevated in both liver and skeletal muscle (P<.05). Hepatic Akt phosphorylation was elevated (P<.05) and FoxO1 protein in hepatic nuclear extracts was reduced (P<.05) in the face of hyperinsulinemia, whereas no increase in Akt phosphorylation or decrease in nuclear FoxO1 was observed in skeletal muscle. Overfeeding increased serum adiponectin concentration from 24.6±1.9 μg/ml to 46.3±5.9 μg/ml (P<.004), and positively correlated with increased adipose tissue mass. The expression of the inflammatory cytokine tumor necrosis factor α in the adipose tissue was unchanged. Adiponectin-mediated adenosine monophosphate (AMP) kinase phosphorylation, peroxisome proliferator-activator receptor-α expression and the expression of genes involved in fatty acid oxidation were elevated in both liver and muscle (P<.05). These data (1) demonstrate that excessive intake of a high-fat diet in young rats results in “adiponectin-independent” increases in ectopic fat deposition and hyperinsulinemia, (2) suggest that fatty acid transport is a major mechanism underlying ectopic fat deposition, (3) demonstrate tissue-specific differences in the response of Akt-FoxO signaling to hyperinsulinemia following the development of pediatric obesity and (4) suggest age-related differences in the role of adiponectin in pathological responses associated with obesity.     

The contribution of GABAergic dysfunction to neurodevelopmental disorders

GABA (γ-aminobutyric acid) is the major inhibitory neurotransmitter in the brain. The GABAergic system is indispensable for maintaining the balance between excitation and inhibition (E/I balance) required for normal neural circuit function. E/I imbalances that result from perturbations in the development of this system, ranging from the generation of inhibitory neurons to the formation of their synaptic connections, have been implicated in several neurodevelopmental disorders. In this review, we discuss how impairments at different stages in GABAergic development can lead to disease states. We also highlight recent studies which show that modulation of the GABAergic system can successfully reverse cognitive deficits in disease models and suggest that therapeutic strategies targeting the GABAergic system could be effective in treating neurodevelopmental disorders.