Dynamic Co-evolution of Peptides and Chemical Energetics, a Gateway to the Emergence of Homochirality and the Catalytic Activity of Peptides

We propose a scenario for the dynamic co-evolution of peptides and energy on the primitive Earth. From a multi component system consisting of hydrogen cyanide, several carbonyl compounds, ammonia, alkyl amine, carbonic anhydride, borate and isocyanic acid, we show that the reversibility of this system leads to several intermediate nitriles, that irreversibly evolve to alpha-amino acids and N-carbamoyl amino acids via selective catalytic processes. On the primitive Earth these N-carbamoyl amino acids combined with energetic molecules (NOx) may have been the core of a molecular engine producing peptides permanently and assuring their recycling and evolution. We present this molecular engine, a production example, and its various selectivities. The perspectives for such a dynamic approach to the emergence of peptides are evoked in the conclusion.     

GH11 xylanases: Structure/function/properties relationships and applications

For technical, environmental and economical reasons, industrial demands for process-fitted enzymes have evolved drastically in the last decade. Therefore, continuous efforts are made in order to get insights into enzyme structure/function relationships to create improved biocatalysts. Xylanases are hemicellulolytic enzymes, which are responsible for the degradation of the heteroxylans constituting the lignocellulosic plant cell wall. Due to their variety, xylanases have been classified in glycoside hydrolase families GH5, GH8, GH10, GH11, GH30 and GH43 in the CAZy database. In this review, we focus on GH11 family, which is one of the best characterized GH families with bacterial and fungal members considered as true xylanases compared to the other families because of their high substrate specificity. Based on an exhaustive analysis of the sequences and 3D structures available so far, in relation with biochemical properties, we assess biochemical aspects of GH11 xylanases: structure, catalytic machinery, focus on their "thumb" loop of major importance in catalytic efficiency and substrate selectivity, inhibition, stability to pH and temperature. GH11 xylanases have for a long time been used as biotechnological tools in various industrial applications and represent in addition promising candidates for future other uses.     

Cellular prion protein electron microscopy: attempts/limits and clues to a synaptic trait. Implications in neurodegeneration process

Prion diseases are caused by an infectious agent constituted by a rogue protein called prion (PrP^Sc) of neuronal origin (PrP^c) and are exemplified by Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy in cattle. Considerable efforts have been made to understand the cerebral damage caused by these diseases but a clear comprehensive view cannot be achieved without defining the neurophysiological function of PrP^c. This lack of information is in part attributable to our ignorance of the precise localization of PrP^c in the brain neuronal cell. One relevant option to explore this aspect is to undertake PrP immunohistochemistry at the electron-microscopy level, knowing that this challenge raises major technical constraints. In describing the attempts and restrictions of the various approaches used, we review here the efforts that have been invested in this particular field of prionology. The common result emerging from these contributions is that the synapse could be the site at which PrP^c exerts its critical activity. This location suggests, in the perspective of synaptic regulation, that PrP^c can be assigned multiple biological functions and supports the novel concept that prion-like changes are involved in long-term memory formation. The synaptic trait of PrP^c and PrP^Sc suggests that synapse loss is the key event in neuronal death. Interestingly, synaptic alterations are also considered to be predominant in the pathophysiological mechanism in Alzheimer, Parkinson and Huntington diseases. All these brain disorders, characterized by the formation of a specific amyloid protein of synaptic origin, can be classified under the heading of amyloidogenic synaptopathies.     

Effects of Hunger on Mate-choice Copying in the Guppy

One potential opportunity cost associated with direct assessment of males by females is lost foraging time. It has been hypothesized previously that females may reduce their mate-assessment time by copying the known mate choice of other females. If mate copying reduces mate-assessment time, then females that engage in copying behaviour should have more time available for foraging. In this study, we experimentally investigated the effects of hunger, and thus the immediate need for energy, on the tendency of female guppies, Poecilia reticulata, to copy the mate choice of others. We manipulated the hunger level of individual females in four different treatments by either depriving them of any food or giving them unlimited access to food for 24 h or 48 h prior to testing their mating preference. Each female was then allowed to choose between two stimulus males, matched for size and colour, after having viewed another female (the model) apparently choose one of the males as a mate. We predicted that hungry female guppies should be more likely to engage in mate-choice copying than more recently fed females, when given the opportunity. Contrary to our a priori prediction, only the most well-fed females (with prior access to feed for 48 h) copied the mate choice of the model female significantly more often than expected by chance. Females in each of the other three treatments chose randomly between the two stimulus males presented.     

Hydrolysis of 4-Hydroxybenzoic Acid Esters (Parabens) and Their Aerobic Transformation into Phenol by the Resistant Enterobacter cloacae Strain EM

Enterobacter cloacae strain EM was isolated from a commercial dietary mineral supplement stabilized by a mixture of methylparaben and propylparaben. It harbored a high-molecular-weight plasmid and was resistant to high concentrations of parabens. Strain EM was able to grow in liquid media containing similar amounts of parabens as found in the mineral supplement (1,700 and 180 mg of methyl and propylparaben, respectively, per liter or 11.2 and 1.0 mM) and in very high concentrations of methylparaben (3,000 mg liter⁻¹, or 19.7 mM). This strain was able to hydrolyze approximately 500 mg of methyl-, ethyl-, or propylparaben liter⁻¹ (3 mM) in less than 2 h in liquid culture, and the supernatant of a sonicated culture, after a 30-fold dilution, was able to hydrolyze 1,000 mg of methylparaben liter⁻¹ (6.6 mM) in 15 min. The first step of paraben degradation was the hydrolysis of the ester bond to produce 4-hydroxybenzoic acid, followed by a decarboxylation step to produce phenol under aerobic conditions. The transformation of 4-hydroxybenzoic acid into phenol was stoichiometric. The conversion of approximately 500 mg of parabens liter⁻¹ (3 mM) to phenol in liquid culture was completed within 5 h without significant hindrance to the growth of strain EM, while higher concentrations of parabens partially inhibited its growth.     

Effects of location of food delivery and social status on foraging-site selection by juvenile Atlantic salmon

Synopsis Experiments were conducted to investigate the response of juvenile Atlantic salmon,Salmo salar, to changes in the location at which food entered a stream tank. Experience with the location of food input into the system significantly influenced foraging-site selection by the dominant fish. Dominant fish changed location of their foraging site in response to a change in the location of food input, and occupied, aggressively defending, sites just downstream of the location of food introduction. In contrast, subordinate fish occupied foraging sites at the downstream end of the stream tank, regardless of location of food input. As a result of both site selection and social status, dominant fish captured significantly more prey than subordinates. Our results support the contention that salmonids choose foraging sites to maximize foraging opportunities. Our results also provide a possible explanation for the use of atypical foraging sites by individual fish within their home range over the course of a single day, as observed in a number of salmonid species in the field.     

Modulation of 3-hydroxy-3-methylglutaryl coenyzyme a (HMG-CoA) reductase activity with intracellular fractions of hamster adrenals

Hamster adrenal HMG-CoA reductase activity was enhanced with rat liver cytosolic phosphorylase phosphatase as well as with similarly isolated beef and hamster adrenal cytosolic preparations. HMG-CoA reductase was inactivated when microsomes were incubated in an EDTA-free medium but containing MgCl₂ and ATP. The reductase activity of microsomes isolated from adrenals of hamsters sacrificed at 1100 h and 1900 h were (mean ± SEM, pmo1/mg protein/min.) 299.6±62.3 and 588.3 ± 96.6 respectively and could be enhanced by a factor of four when preincubated in the presence of liver phosphatase.     

Une nouvelle méthode de marquage pour certains groupes d'Insectes et de Crustacés

A new technique of labelling, based on making series of microscars on the compound eye of immature insects, allows to recognize individual specimens, even after several moults.

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Une nouvelle méthode de marquage pour certains groupes d'Insectes et de Crustacés