Architecture of the eIF2B regulatory subcomplex and its implications for the regulation of guanine nucleotide exchange on eIF2

Eukaryal translation initiation factor 2B (eIF2B) acts as guanine nucleotide exchange factor (GEF) for eIF2 and forms a central target for pathways regulating global protein synthesis. eIF2B consists of five non-identical subunits (α–ϵ), which assemble into a catalytic subcomplex (γ, ϵ) responsible for the GEF activity, and a regulatory subcomplex (α, β, δ) which regulates the GEF activity under stress conditions. Here, we provide new structural and functional insight into the regulatory subcomplex of eIF2B (eIF2B^RSC). We report the crystal structures of eIF2Bβ and eIF2Bδ from Chaetomium thermophilum as well as the crystal structure of their tetrameric eIF2B(βδ)₂ complex. Combined with mutational and biochemical data, we show that eIF2B^RSC exists as a hexamer in solution, consisting of two eIF2Bβδ heterodimers and one eIF2Bα₂ homodimer, which is homologous to homohexameric ribose 1,5-bisphosphate isomerases. This homology is further substantiated by the finding that eIF2Bα specifically binds AMP and GMP as ligands. Based on our data, we propose a model for eIF2B^RSC and its interactions with eIF2 that is consistent with previous biochemical and genetic data and provides a framework to better understand eIF2B function, the molecular basis for Gcn⁻, Gcd⁻ and VWM/CACH mutations and the evolutionary history of the eIF2B complex.     

Structural and Biochemical Basis for the Inhibitory Effect of Liprin-α3 on Mouse Diaphanous 1 (mDia1) Function

Diaphanous-related formins are eukaryotic actin nucleation factors regulated by an autoinhibitory interaction between the N-terminal RhoGTPase-binding domain (mDia_N) and the C-terminal Diaphanous-autoregulatory domain (DAD). Although the activation of formins by Rho proteins is well characterized, its inactivation is only marginally understood. Recently, liprin-α3 was shown to interact with mDia1. Overexpression of liprin-α3 resulted in a reduction of the cellular actin filament content. The molecular mechanisms of how liprin-α3 exerts this effect and counteracts mDia1 activation by RhoA are unknown. Here, we functionally and structurally define a minimal liprin-α3 core region, sufficient to recapitulate the liprin-α3 determined mDia1-respective cellular functions. We show that liprin-α3 alters the interaction kinetics and thermodynamics of mDia_N with RhoA·GTP and DAD. RhoA displaces liprin-α3 allosterically, whereas DAD competes with liprin-α3 for a highly overlapping binding site on mDia_N. Liprin-α3 regulates actin polymerization by lowering the regulatory potency of RhoA and DAD on mDia_N. We present a model of a mechanistically unexplored and new aspect of mDia_N regulation by liprin-α3.     

Diet quality and immunocompetence influence parasite load of roe deer in a fragmented landscape

The influence of landscape structure and host diet on parasite load of wildlife is still largely unknown. We studied a roe deer (Capreolus capreolus) population in a fragmented agricultural landscape in southern France to explore the relationship of gastrointestinal nematode load with spleen mass (to index immunocompetence), faecal nitrogen (to index diet quality), landscape structure and age of 33 hunt-harvested roe deer. Gastrointestinal worm counts were negatively related to faecal nitrogen and spleen mass, explaining respectively 24.7% and 9.2% of the observed variability in parasite load. Landscape structure did not appear to have a direct influence on gastrointestinal worm counts, but since animals from more open areas have a diet that is richer in nitrogen, its influence may be indirect. In conclusion, in the study area, the colonisation of the agricultural landscape does not seem to have increased the risk of gastrointestinal nematode parasitism for roe deer, possibly because access to high-quality food enhances immunocompetence.

     

Biodiversity, evolution and adaptation of cultivated crops

The human diet depends on very few crops. Current diversity in these crops is the result of a long interaction between farmers and cultivated plants, and their environment. Man largely shaped crop biodiversity from the domestication period 12,000 B.P. to the development of improved varieties during the last century. We illustrate this process through a detailed analysis of the domestication and early diffusion of maize. In smallholder agricultural systems, farmers still have a major impact on crop diversity today. We review several examples of the major impact of man on current diversity. Finally, biodiversity is considered to be an asset for adaptation to current environmental changes. We describe the evolution of pearl millet in West Africa, where average rainfall has decreased over the last forty years. Diversity in cultivated varieties has certainly helped this crop to adapt to climate variation.     

Genotype and ancestry modulate brain's DAT availability in healthy humans

The dopamine transporter (DAT) is a principal regulator of dopaminergic neurotransmission and its gene (the SLC6A3) is a strong biological candidate gene for various behavioral- and neurological disorders. Intense investigation of the link between the SLC6A3 polymorphisms and behavioral phenotypes yielded inconsistent and even contradictory results. Reliance on objective brain phenotype measures, for example, those afforded by brain imaging, might critically improve detection of DAT genotype-phenotype association. Here, we tested the relationship between the DAT brain availability and the SLC6A3 genotypes using an aggregate sample of 95 healthy participants of several imaging studies. These studies employed positron emission tomography (PET) with [11C]cocaine wherein the DAT availability was estimated as Bmax/Kd; while the genotype values were obtained on two repeat polymorphisms--3-UTR- and intron 8--VNTRs. The main findings are the following: 1) both polymorphisms analyzed as single genetic markers and in combination (haplotype) modulate DAT density in midbrain; 2) ethnic background and age influence the strength of these associations; and 3) age-related changes in DAT availability differ in the 3-UTR and intron 8--genotype groups.     

Characterization of an oxidoreductase from the arylamine N-acetyltransferase operon in Mycobacterium smegmatis

Mycobacterium?tuberculosis, the most successful bacterial pathogen, causes tuberculosis, a disease that still causes more than 2 million deaths per year. Arylamine N-acetyltransferase is an enzyme that is conserved in most Mycobacterium spp. The nat gene belongs to an operon that is important for the intracellular survival of M. tuberculosis within macrophages. The nat operon in Mycobacterium smegmatis and other fast-growing mycobacterial species has a unique organization containing genes with uncharacterized function. Here, we describe the biochemical, biophysical and structural characterization of the MSMEG_0308 gene product (MS0308) of the M. smegmatis nat operon. While characterizing the function of MS0308, we validated the oxidoreductase property; however, we found that the enzyme was not utilizing dihydrofolate as its substrate, hence we first report that MS0308 is not a dihydrofolate reductase, as annotated in the genome. The structure of this oxidoreductase was solved at 2.0 ? in complex with the cofactor NADPH and has revealed the hydrophobic pocket where the endogenous substrate binds.     

Enhanced striatal dopamine release during food stimulation in binge eating disorder

Subjects with binge eating disorder (BED) regularly consume large amounts of food in short time periods. The neurobiology of BED is poorly understood. Brain dopamine, which regulates motivation for food intake, is likely to be involved. We assessed the involvement of brain dopamine in the motivation for food consumption in binge eaters. Positron emission tomography (PET) scans with [(11)C]raclopride were done in 10 obese BED and 8 obese subjects without BED. Changes in extracellular dopamine in the striatum in response to food stimulation in food-deprived subjects were evaluated after placebo and after oral methylphenidate (MPH), a drug that blocks the dopamine reuptake transporter and thus amplifies dopamine signals. Neither the neutral stimuli (with or without MPH) nor the food stimuli when given with placebo increased extracellular dopamine. The food stimuli when given with MPH significantly increased dopamine in the caudate and putamen in the binge eaters but not in the nonbinge eaters. Dopamine increases in the caudate were significantly correlated with the binge eating scores but not with BMI. These results identify dopamine neurotransmission in the caudate as being of relevance to the neurobiology of BED. The lack of correlation between BMI and dopamine changes suggests that dopamine release per se does not predict BMI within a group of obese individuals but that it predicts binge eating.