Structural effects of point mutations in proteins

A structural database of 11 families of chains differing by a single amino acid substitution has been built. Another structural dataset of 5 families with identical sequences has been used for comparison. The RMSD computed after a global superimposition of the mutated protein on each native one is smaller than the RMSD calculated among proteins of identical sequences. The effect of the perturbation is very local, and not necessarily the highest at the position of the mutation. A RMSD between mutated and native proteins is computed over a 3‐residue or a 7‐residue window at each position. To separate the effects of structural fluctuations due to point mutations from other sources, pair RMSD have been translated into P values which themselves are included in a score called P‐RANK. This score allows highlighting small backbone distortions by comparing these RMSD between mutated and native positions to the RMSD at the same positions in the absence of a mutation. It results from the P‐RANK that 38% of all mutations produce a significant effect on the displacement. When compared with a random distribution of RMSD at un‐mutated positions, we show that, even if the RMSD is greater when the mutation is in loops than in regular secondary structure, the relative effect is more important for regular secondary structures and for buried positions. We confirm the absence of correlation between RMSD and the predicted variation of free energy of folding but we found a small correlation between high RMSD and the error in the prediction of ΔΔG.     

New phenylaniline derivatives as modulators of amyloid protein precursor metabolism

The chloroquinoline scaffold is characteristic of anti-malarial drugs such as chloroquine (CQ) or amodiaquine (AQ). These drugs are also described for their potential effectiveness against prion disease, HCV, EBV, Ebola virus, cancer, Parkinson or Alzheimer diseases. Amyloid precursor protein (APP) metabolism is deregulated in Alzheimer’s disease. Indeed, CQ modifies amyloid precursor protein (APP) metabolism by precluding the release of amyloid-beta peptides (Aβ), which accumulate in the brain of Alzheimer patients to form the so-called amyloid plaques. We showed that AQ and analogs have similar effects although having a higher cytotoxicity. Herein, two new series of compounds were synthesized by replacing 7-chloroquinolin-4-amine moiety of AQ by 2-aminomethylaniline and 2-aminomethylphenyle moieties. Their structure activity relationship was based on their ability to modulate APP metabolism, Aβ release, and their cytotoxicity similarly to CQ. Two compounds 15a, 16a showed interesting and potent effect on the redirection of APP metabolism toward a decrease of Aβ peptide release (in the same range compared to AQ), and a 3–10-fold increased stability of APP carboxy terminal fragments (CTFα and AICD) without obvious cellular toxicity at 100?µM.     

Dissecting complex physiological functions through the use of molecular quantitative genetics

Testing possible associations between physiological and biochemicaltraits by comparing plant phenotypes and looking for correlationsbetween them is unreliable. The development of molecular markertechnologies offers powerful alternative methods to examinethe relationships between traits. This review describes thegenetical methods required to analyse possible associationsbetween traits that are inherited in a quantitative manner usingquantitative trait locus (QTL) analysis. The regulation of carbohydratemetabolism is chosen as an example of how QTL analysis can beused to identify key control factors in a series of processes,by identifying possible candidate genes for QTL effects on sucroseand starch metabolism. Methods are also described to study theassociation between physiological traits such as abscislc acidconcentrations and stomata1 conductance. Advantages and somelimitations of QTL analysis over other methods currently inuse by physiologists to test associations between traits arediscussed. Key words: Candidate genes, genetic maps, molecular markers, quantitative trait locus (QTL) analysis, physiological traits     

Effects of rain forest disturbance and fragmentation: comparative changes of the raptor community along natural and human-made gradients in French Guiana

A density index of every diurnal raptor species (Falconiformes) was obtained on 101 400 ha sample plots distributed among eight natural habitats and five man-made habitats arranged along gradients of increasing forest degradation and fragmentation. The most significant structural parameter affecting species distribution was the tall canopy forest cover. Species richness, diversity and density all decreased with this mature forest cover index. Individual species and overall community densities decreased along the deforestation gradient but the species richness was partly maintained by species turnover. Six groups of species were identified according to their natural habitat preferences. Their distribution along the deforestation gradient was correlated with their natural habitat selection pattern. Thus the community composition of each vegetation or landscape type was predictable. Fifty-six percent of the regional assemblage of species had their optimal density in the primary forest. A third of them were interior forest species highly sensitive to forest disturbance and opening. The other two-thirds were upper canopy, gap or edge species more tolerant to forest fragmentation. The last twenty-one species were associated with various coastal habitats, from dense forest patches to mangrove and savanna. Again, one third of them were strictly restricted to their specialized habitats while the last two-thirds colonized human-altered habitats and progressively replaced primary forest species with increasing deforestation. The maintenance of large areas of every natural habitat was essential for the conservation of (1) the whole population of a third of the total raptor diversity and (2) optimal and presumably potential source populations of most other species surviving in human-modified habitats.     

Metabolic engineering of astaxanthin biosynthesis in maize endosperm and characterization of a prototype high oil hybrid

Maize was genetically engineered for the biosynthesis of the high value carotenoid astaxanthin in the kernel endosperm. Introduction of a β-carotene hydroxylase and a β-carotene ketolase into a white maize genetic background extended the carotenoid pathway to astaxanthin. Simultaneously, phytoene synthase, the controlling enzyme of carotenogenesis, was over-expressed for enhanced carotenoid production and lycopene ε-cyclase was knocked-down to direct more precursors into the β-branch of the extended ketocarotenoid pathway which ends with astaxanthin. This astaxanthin-accumulating transgenic line was crossed into a high oil- maize genotype in order to increase the storage capacity for lipophilic astaxanthin. The high oil astaxanthin hybrid was compared to its astaxanthin producing parent. We report an in depth metabolomic and proteomic analysis which revealed major up- or down- regulation of genes involved in primary metabolism. Specifically, amino acid biosynthesis and the citric acid cycle which compete with the synthesis or utilization of pyruvate and glyceraldehyde 3-phosphate, the precursors for carotenogenesis, were down-regulated. Nevertheless, principal component analysis demonstrated that this compositional change is within the range of the two wild type parents used to generate the high oil producing astaxanthin hybrid.     

Escherichia coli Population Structure and Antibiotic Resistance at a Buffalo/Cattle Interface in Southern Africa

At a human/livestock/wildlife interface, Escherichia coli populations were used to assess the risk of bacterial and antibiotic resistance dissemination between hosts. We used phenotypic and genotypic characterization techniques to describe the structure and the level of antibiotic resistance of E. coli commensal populations and the resistant Enterobacteriaceae carriage of sympatric African buffalo (Syncerus caffer caffer) and cattle populations characterized by their contact patterns in the southern part of Hwange ecosystem in Zimbabwe. Our results (i) confirmed our assumption that buffalo and cattle share similar phylogroup profiles, dominated by B1 (44.5%) and E (29.0%) phylogroups, with some variability in A phylogroup presence (from 1.9 to 12%); (ii) identified a significant gradient of antibiotic resistance from isolated buffalo to buffalo in contact with cattle and cattle populations expressed as the Murray score among Enterobacteriaceae (0.146, 0.258, and 0.340, respectively) and as the presence of tetracycline-, trimethoprim-, and amoxicillin-resistant subdominant E. coli strains (0, 5.7, and 38%, respectively); (iii) evidenced the dissemination of tetracycline, trimethoprim, and amoxicillin resistance genes (tet, dfrA, and bla_TEM-1) in 26 isolated subdominant E. coli strains between nearby buffalo and cattle populations, that led us (iv) to hypothesize the role of the human/animal interface in the dissemination of genetic material from human to cattle and toward wildlife. The study of antibiotic resistance dissemination in multihost systems and at anthropized/natural interface is necessary to better understand and mitigate its multiple threats. These results also contribute to attempts aiming at using E. coli as a tool for the identification of pathogen transmission pathway in multihost systems.     

Studien über die Biologie des Erregers der Schrotschußkrankheit des Steinobstes (Clasterosporium carpophilum Aderhold) und über die Aussichten einer Züchtung schrotschußresistenter Sauerkirschensorten.

Theoretical and Applied Genetics -