Salt bridges at the inter-ring interface regulate the thermostat of GroEL

The chaperonin GroEL consists of a double-ring structure made of identical subunits and displays unusual allosteric properties caused by the interaction between its constituent subunits. Cooperative binding of ATP to a protein ring allows binding of GroES to that ring, and at the same time negative inter-ring cooperativity discharges the ligands from the opposite ring, thus driving the protein-folding cycle. Biochemical and electron microscopy analysis of wild type GroEL, a single-ring mutant (SR1), and two mutants with one inter-ring salt bridge of the chaperonin disrupted (E461K and E434K) indicate that these ion pairs form part of the interactions that allow the inter-ring allosteric signal to be transmitted. The wild type-like activities of the ion pair mutants at 25 degrees C are in contrast with their lack of inter-ring communication and folding activity at physiological temperatures. These salt bridges stabilize the inter-ring interface and maintain the inter-ring spacing so that functional communication between protein heptamers takes place. The characterization of GroEL hybrids containing different amounts of wild type and mutant subunits also indicates that as the number of inter-ring salt bridges increases the functional properties of the hybrids recover. Taken together, these results strongly suggest that inter-ring salt bridges form a stabilizing ring-shaped, ionic zipper that ensures inter-ring communication at the contact sites and therefore a functional protein-folding cycle. Furthermore, they regulate the chaperonin thermostat, allowing GroEL to distinguish physiological (37 degrees C) from stress temperatures (42 degrees C).     

Modulation of Higher-Order Olfaction Components on Executive Functions in Humans

The prefrontal (PFC) and orbitofrontal cortex (OFC) appear to be associated with both executive functions and olfaction. However, there is little data relating olfactory processing and executive functions in humans. The present study aimed at exploring the role of olfaction on executive functioning, making a distinction between primary and more cognitive aspects of olfaction. Three executive tasks of similar difficulty were used. One was used to assess hot executive functions (Iowa Gambling Task-IGT), and two as a measure of cold executive functioning (Stroop Colour and Word Test-SCWT and Wisconsin Card Sorting Test-WCST). Sixty two healthy participants were included: 31 with normosmia and 31 with hyposmia. Olfactory abilities were assessed using the ‘‘Sniffin’ Sticks’’ test and the olfactory threshold, odour discrimination and odour identification measures were obtained. All participants were female, aged between 18 and 60. Results showed that participants with hyposmia displayed worse performance in decision making (IGT; Cohen’s-d = 0.91) and cognitive flexibility (WCST; Cohen’s-d between 0.54 and 0.68) compared to those with normosmia. Multiple regression adjusted by the covariates participants’ age and education level showed a positive association between odour identification and the cognitive inhibition response (SCWT-interference; Beta = 0.29; p = .034). The odour discrimination capacity was not a predictor of the cognitive executive performance. Our results suggest that both hot and cold executive functions seem to be associated with higher-order olfactory functioning in humans. These results robustly support the hypothesis that olfaction and executive measures have a common neural substrate in PFC and OFC, and suggest that olfaction might be a reliable cognitive marker in psychiatric and neurologic disorders.     

Paradoxical effects of a stress signal on pro- and anti-apoptotic machinery in HTLV-1 tax expressing cells

Adult T-cell leukemia (ATL) and HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP) are associated with Human T-cell lymphotropic virus type 1 (HTLV-1) infection. The viral transactivator, Tax is able to mediate the cell cycle progression by targeting key regulators of the cell cycle such as p21/waf1, p16/ink4a, p53, cyclins D1-3/cdk complexes, and the mitotic spindle checkpoint MAD apparatus, thereby deregulating cellular DNA damage and checkpoint control. Genome expression profiling of infected cells exemplified by the development of DNA microarrays represents a major advance in genome-wide functional analysis. Utilizing cDNA microarray analysis, we have observed an apparent opposing and paradoxical regulatory network of host cell gene expression upon the introduction of DNA damage stress signal. We find the apparent induction of cell cycle inhibitors, and pro- as well as anti-apoptotic gene expression is directly linked to whether cells are at either G1, S, or G2/M phases of the cell cycle. Specifically, a G1/S block is induced by p21/waf1 and p16/ink4a, while pro-apoptotic expression at S, and G2/M is associated with caspase activation, and anti-apoptotic gene expression is associated with up regulation of Bcl-2 family member, namely bfl-1 gene. Therefore, the microarray results indicating expression of both pro- and anti-apoptotic genes could easily be explained by the particular stage of the cell cycle. Mechanism and the functional outcome of induction for both pathways are discussed.     

Seasonal Variation of Antifouling Activities of Marine Algae from the Brittany Coast (France)

The antifouling activity of extracts (aqueous, ethanol, and dichloromethane) of 9 marine macroalgae against bacteria, fungi, diatoms, macroalgal spores, mussel phenoloxidase activity, and barnacle cypris larvae has been investigated in relation to season in bimonthly samples from the Bay of Concarneau (France). Of the extracts tested, 48.2% were active against at least one of the fouling organisms, and of these extracts, 31.2% were seasonally active with a peak of activity in summer corresponding to maximal values for water temperature, light intensity, and fouling pressure, and 17% were active throughout the year. This seasonal activity may be adaptive as it coincides with maximal fouling pressure in the Bay of Concarneau. Dichloromethane extracts of Rhodophyceae were the most active in the antifouling assays.     

Fruit infesting tephritids [Dipt.: Tephritidae] and associated parasitoids in Chiapas,Mexico

A total of 1,302 parasitoids representing 8 species and 4 families were recovered from 9,818 fruit fly host fruits sampled. The most common parasitoid species wasDiachasmimorpha longicaudata (Ashmead). Average percent parasitism ranged between 0.44 and 29.23%. Parasitoid emergence data indicate thatAnastrepha ludens (Loew),A. obliqua (Sein),A. serpentina (Wiedeman),A. striata (Schiner) andToxotrypana curvicauda (Gerstaecker) were subject to parasitism. We provide information on the population fluctuation ofAnastrepha ludens, A. obliqua, A. serpentina, A. distincta (Greene),A. striata, A. fraterculus (Wiedeman),A. chiclayae (Greene),A. montei (Costa Lima),A. leptozona (Hendel) andA. tripunctata (Wulp).Anastrepha ludens andA. obliqua were the most common species, representing 95.3% of all fruit fly species caught in McPhail traps.      

The structure of Erb1-Ytm1 complex reveals the functional importance of a high-affinity binding between two β-propellers during the assembly of large ribosomal subunits in eukaryotes

Ribosome biogenesis is one of the most essential pathways in eukaryotes although it is still not fully characterized. Given the importance of this process in proliferating cells, it is obvious that understanding the macromolecular details of the interactions that take place between the assembly factors, ribosomal proteins and nascent pre-rRNAs is essentially required for the development of new non-genotoxic treatments for cancer. Herein, we have studied the association between the WD40-repeat domains of Erb1 and Ytm1 proteins. These are essential factors for the biogenesis of 60S ribosomal subunits in eukaryotes that form a heterotrimeric complex together with the also essential Nop7 protein. We provide the crystal structure of a dimer formed by the C-terminal part of Erb1 and Ytm1 from Chaetomium thermophilum at 2.1 Å resolution. Using a multidisciplinary approach we show that the β-propeller domains of these proteins interact in a novel manner that leads to a high-affinity binding. We prove that a point mutation within the interface of the complex impairs the interaction between the two proteins and negatively affects growth and ribosome production in yeast. Our study suggests insights into the association of the Erb1-Ytm1 dimer with pre-ribosomal particles.     

Membrane interactions of ionic liquids: Possible determinants for biological activity and toxicity

Ionic liquids (ILs) are a class of diverse organic salts with relatively low melting points (below 100°C) which have attracted considerable interest as a promising "green" substitute for organic solvents. The broad solvation properties of ILs and their high solubility in water, however, present health risks, in particular since it was shown that many ILs exhibit cytotoxic properties. In this context, interactions of ILs with the cellular membrane are believed to constitute a primary culprit for toxicity. We present a comprehensive biophysical and microscopy study of membrane interactions of a series of ILs having different side-chain compositions and lengths, and cationic head-group structures and orientations. The experimental data reveal that the ILs studied exhibit distinct mechanisms of membrane binding, insertion, and disruption which could be correlated with their biological activities. The results indicate, in particular, that both the side chain composition and particularly the head-groups of ILs constitute determinants for membrane activity and consequent cell toxicity. This work suggests that tuning membrane interactions of ILs should be an important factor for designing future compounds with benign environmental impact.     

The reserve proteins in the cells of mature cotyledons ofLupinus albus var.Lucky

Summary The nuclear DNA content of cotyledonary cells of two lupin seeds (L₁ and L₂) with markedly different total protein content, were investigated by scanning cytophotometry. Both seeds had polyloid nuclei with DNA levels varying between 8 C and 64 C, the majority being either 16 C or 32 C. The highest DNA levels were found in the abaxial and central cotyledonary zones of both seeds; seed L₂ had a higher ploidy level than L₁. It is shown that the volume of condensed chromatin (chromocenters) increased proportionally with the DNA content of the nucleus. A comparison was made between the distribution of protein, previously determined byLe Gal andRey (1986) and the DNA throughout the cotyledon. The L₂ seed, which has the highest total protein and the highest protein content per cell, also exhibited the greatest DNA content per cell. For both seeds, the r-value for association of DNA and protein content per cell was highly significant (0.98).