Stereoselective disulfide formation stabilizes the local peptide conformation in nisin mimics

Nisin is a polymacrocyclic peptide antimicrobial with high activity against Gram-positive bacteria. Lanthionine and methyllanthionine bridges, closing the macrocycles, are stabilized by thioether bonds, formed between cysteines and dehydrated serine or threonine. The role of polypeptide backbone conformation in the formation of macrocycles A and B within cysteine mutants of nisin residues 1?12 is investigated here by molecular dynamics simulations. Enantiomeric combinational space of Cys3 and Cys7 and of Cys8 and Cys11 is examined for the preference of disulfide bond formation over helical turn formation within this region. A clear preference for spontaneous disulfide formation and closure of rings 3,7 and 8,11 is demonstrated for the D-Cys3, D-Cys7, L-Cys8, L-Cys11 nisin homologue, while interlinked rings A and B are obtained through disulfide bridges between L-Cys3 and D-Cys8 and between D-Cys7 and D-Cys11. This study offers a simple designer approach to solid phase synthesis of macrocyclic peptides and lantibiotic analogues.     

Resistance to Melanaphis sacchari in the sugarcane cultivar R 365

This study focuses on the resistance of sugarcane, Saccharum spec. (Poaceae), to the sugarcane aphid, Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae), which vectors Sugarcane yellow leaf virus (SCYLV). Resistance was characterized in cultivar R 365, using a 3‐year field trial and laboratory experiments on potted plantlets and excised leaves. R 365 reduced aphid populations in the field by antixenosis and antibiosis. Using the electrical penetration graph technique, we detected delayed aphid salivation in phloem and inhibition of passive phloem sap uptake in R 365. The resistance factors also proved to be effective against the corn leaf aphid, Rhopalosiphum maidis (Fitch) (Hemiptera: Aphididae), another vector of SCYLV.     

Temporal Variation in Seed Predation by Insects in a Population of Syagrus romanzoffiana (Arecaceae) in Santa Catarina Island, SC, Brazil

Insect seed predation may vary depending on seed production. The present study considers the hypothesis that the rates of seed predation tend to be smaller in years of higher fruit production. Thus, we monitored the production of fruits and predation of seeds of the palm Syagrus romanzoffiana over 2?years in the Atlantic Forest (Parque Municipal da Lagoa do Peri, Florianópolis, SC, Brazil), between July 2006 and June 2008. Plots of 0.25?m² were fitted under 20 mother plants and fruits were monthly collected for assessment of abundance and seed predation. There was variation in fruit production between the 2?years and among reproductive plants. Predation rates were high and occurred in the predispersal phase by the Curculionidae Revena rubiginosa Boheman, Anchylorhynchus aegrotus Fahraeus, and Anchylorhynchus variabilis Gyllenhal. Seed predation by these species of Anchylorhynchus is first registered in the present study. In average, about 60% of the seeds monthly produced in the population tend to escape insect predation in year of high or low production, becoming available for recruitment. The predation rate was not related to the amount of fruits produced per reproductive plant. Also, different than expected, there was a positive relation between the rates of seed predation and the total of fruits produced monthly on the plots. Thus, no evidence for the satiation of insect seed predators was found in this study with S. romanzoffiana.     

Motor and psycho-cognitive clinical types in adult metachromatic leukodystrophy: genotype/phenotype relationships?

Metachromatic leukodystrophy (MLD) is a recessive autosomal disease which is biochemically characterized by an accumulation of sulfatides (sulfogalactosylceramides) mainly in oligodendrocytes and macrophages/microglia. The deficient enzyme is a lysosomal hydrolase, cerebroside sulfate sulfatase (arylsulfatase A). MLD is both a dysmyelinating and a demyelinating disease. The main clinical forms are infantile or juvenile, but some forms appear at adulthood. This disease involves also neuronal cells as sulfatides are also present in neurons in which the defect in degradation occurs also. We have studied 12 cases of adult MLD and clearly distinguished two clinical forms. One of them was characterized by mainly central nervous system motor signs (pyramidal, cerebellar, and seldom dystonia) and a peripheral neuropathy. The other form always started by behavioural abnormalities with modifications of mood, peculiar social reactions; a progressive mental deterioration occurred also. The diagnosis of schizophrenia was often mentioned. Most of these patients remained for many years without any neurological symptoms, and the diagnosis was only made when neurological signs appeared, or when Magnetic Resonance Imaging (MRI) was performed. MRI showed a diffuse demyelination, bilateral and often symmetrical, which could be temporarily limited to the periventricular areas. The diagnosis of adult MLD was biochemical, evidencing the low activity of arylsulfatase A (ASA) and sulfatide accumulation. To determine the respective participation of neurons and glial cells in the physiopathology of both the motor forms and the psycho-cognitive forms, our first approach was to search for mutations differing according to the clinical status. Motor forms involved the major adult ASA mutation P426L in a homozygote form in contrast to psycho-cognitive forms which involved as a compound heterozygote a specific I179S mutation.     

An ion-exchange based extraction method for the detection of salmonellas in soil

A method that uses a cation-exchange resin (Chelex 100) and differential centrifugation for the extraction and detection of salmonellas in soil was developed. The extraction efficiencies of a range of materials were examined and Chelex plus polyethylene glycol was identified as the best combination. Shake speeds, shake times and differential centrifugation speeds were selected to give an optimum salmonella recovery. The Chelex method accurately enumerated 1 cell per 10 g of nonsterile soil within 24 h. Addition of glycerol to soil samples enabled storage at — 70°C for 85 d without significant decreases in salmonella numbers. The Oxoid Salmonella Rapid Test (SRT) could be used to pre-screen large numbers of soil samples for the presence of salmonellas, prior to analysis by the Chelex method. The SRT method detected Salmonella typhimurium at levels as low as 2·5 cells per 10 g of nonsterile soil.     

Confidence intervals for predicted age of onset,given the size of (CAG) n repeat,in Huntington's disease

A highly significant relationship between length of trinucleotide repeat and age of onset is shown for Huntington's disease.     

Gramicidin S Synthetase,an Enzyme with an Unusually Large Number of Catalytic Functions

THE biosynthesis of gramicidin S consists in joining five different amino-acids, each occurring twice, into the cyclic structure: illustration

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