A three-dimensional homology model of the O-acetylserine sulfhydrylase-B from Salmonella typhimurium

O-acetylserine sulfhydrylase (OASS) catalyzes the last step in the cysteine biosynthetic pathway in enteric bacteria and plants. The overall pathway involves the substitution of the beta-acetoxy group of O-acetyl-L-serine with inorganic bisulfide. Two isozymes are present in S. typhimurium, the A- and B-isozymes, expressed under aerobic and anaerobic conditions, respectively. No crystal structure is presently available for the B-isozyme. Kinetic data indicate the catalytic mechanism of OASS-B is ping-pong, as found for the A-isozyme, but kinetic parameters and substrate specificity differ. In order to estimate whether structural differences may be responsible for the kinetic differences, a homology model was built using the structure of OASS-A as the template for the OASS-B model. The beta-subunit of tryptophan synthase and cystathionine beta-synthase were used for comparison. Differences between the OASS-A structure and the homology model for OASS-B are discussed.     

Quantitative trait loci for grain fructan concentration in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Fructans (fructo-oligosaccharides) are prebiotics that are thought to selectively promote the growth of colonic bifidobacteria, thereby improving human gut health. Fructans are present in the grain of wheat, a staple food crop. In the research reported here, we aimed to detect and map loci affecting grain fructan concentration in wheat using a doubled-haploid population derived from a cross between a high-fructan breeding line, Berkut, and a low-fructan cultivar, Krichauff. Fructan concentration was measured in grain samples grown at two locations in Australia and one in Kazakhstan. Fructan concentration varied widely within the population, ranging from 0.6 to 2.6% of grain dry weight, and was quite repeatable, with broad-sense heritability estimated as 0.71. With a linkage map of 528 molecular markers, quantitative trait loci (QTLs) were detected on chromosomes 2B, 3B, 5A, 6D and 7A. Of these, the QTLs on chromosomes 6D and 7A had the largest effects, explaining 17 and 27% of the total phenotypic variance, respectively, both with the favourable (high-fructan concentration) alleles contributed from Berkut. These chromosome regions had similar effects in another mapping population, Sokoll/Krichauff, with the favourable alleles contributed from Sokoll. It is concluded that grain fructan concentration of wheat can be improved by breeding and that molecular markers could be used to select effectively for favourable alleles in two regions of the wheat genome.     

Hyperinsulinemia fails to augment ET-1 action in the skeletal muscle vascular bed in vivo in humans

Endogenous endothelin action is augmented in human obesity and type 2 diabetes and contributes to endothelial dysfunction and impairs insulin-mediated vasodilation in humans. We hypothesized that insulin resistance-associated hyperinsulinemia could preferentially drive endothelin-mediated vasoconstriction. We applied hyperinsulinemic-euglycemic clamps with higher insulin dosing in obese subjects than lean subjects (30 vs. 10 mU.m(-2).min(-1), respectively), with the goal of matching insulin's nitric oxide (NO)-mediated vascular effects. We predicted that, under these circumstances, insulin-stimulated endothelin-1 (ET-1) action (assessed with the type A endothelin receptor antagonist BQ-123) would be augmented in proportion to hyperinsulinemia. NO bioactivity was assessed using the nitric oxide synthase inhibitor N(G)-monomethyl-l-arginine. Insulin-mediated vasodilation and insulin-stimulated NO bioavailability were well matched across groups by this approach. As expected, steady-state insulin levels were approximately threefold higher in obese than lean subjects (109.2 +/- 10.2 pmol/l vs. 518.4 +/- 84.0, P = 0.03). Despite this, the augmentation of insulin-mediated vasodilation by BQ-123 was not different between groups. ET-1 flux across the leg was not augmented by insulin alone but was increased with the addition of BQ-123 to insulin (P = 0.01 BQ-123 effect, P = not significant comparing groups). Endothelin antagonism augmented insulin-stimulated NO bioavailability and NOx flux, but not differently between groups and not proportional to hyperinsulinemia. These findings do not support the hypothesis that insulin resistance-associated hyperinsulinemia preferentially drives endothelin-mediated vasoconstriction.     

Effectiveness of selective genotyping for detection of quantitative trait loci: an analysis of grain and malt quality traits in three barley populations.

Marker genotype data and grain and malt quality phenotype data from three barley (Hordeum vulgare L.) mapping populations were used to investigate the feasibility of selective genotyping for detection of quantitative trait loci (QTLs). With selective genotyping, only individuals with high and low phenotypic values for the trait of interest are genotyped. Here, genotyping of 10 to 70% of each population (i.e., 5 to 35% in each tail of the phenotypic distribution) was considered. Genomic positions detected by selective genotyping were compared to QTL position estimates from interval mapping analysis using marker genotype data from the entire population. Selective genotyping reliably detected almost all of the mapped QTLs, often with only 10% of the population genotyped. Selective genotyping also detected spurious QTLs in regions of the genome where no significant QTL had been mapped. Even with additional genotyping to verify putative QTLs, the total genotyping effort for detection of QTLs for a single trait by selective genotyping was usually less than 30% of that required for conventional interval mapping. Simultaneous investigation of two or more traits by selective genotyping would require additional genotyping effort, but could still be worthwhile.     

'Home' choice and modification by juvenile Octopus vulgaris (Mollusca: Cephalopoda): specialized intelligence and tool use?

Analysis of 'homes' occupied by juvenile Octopus vulgaris shows flexible behaviour which may indicate specialized intelligence and tool use. Octopuses occupied sheltered areas for a short time, average 10 days, but stayed longer in larger homes and in areas where preferred prey was available. They did not simply respond to perceptual characteristics of a site, but instead chose locations potentially suitable and modified them by removing rocks and sand and bringing in items partially to block the aperture.     

Vox alouattinae: A preliminary survey of the acoustic characteristics of long-distance calls of howling monkeys

This survey of the acoustic characteristics of howling monkey loud calls, covering six of the seven members of the genus Alouattaand presenting audiospectrograms of roars from two species for the first time, suggests that the genus consists of at least two groups: a monotypic palliatagroup, including all subspecies, and a non-palliatagroup, including belzebul, caraya, fusca, pigra,and seniculus.The non-palliatagroup vocalizes continuously for sustained periods of time;their loud calls exhibit a wide bandwidth relative to the calls of the palliatagroup, with emphasized frequencies generally in the range 300- 2000 Hz. The palliatagroup does not vocalize continuously, their vocal bouts being significantly shorter than those of the non-palliataforms. The emphasized frequencies are normally restricted to 300- 1000 Hz, with little acoustic energy in higher frequencies. This bipartite classification places pigrawithin the non-palliatagroup father than with parapatric palliata,which may have important phylogenetic implications. Further, the classification suggests two modes of employing the highly derived howler vocal tract to produce loud calls within the portion of the ambient noise spectrum favorable to long- distance transmission of sound. Finally, I discuss the constraints placed by environmental acoustics on strategies for long- distance communication, hypothesized modes of vocal production, and the use of acoustic studies for phylogenetic reconstruction. Each discussion suggests projects, some already under way, that could elucidate the determinants of variations in communicative patterns within specific social and physical environments.     

Resistance to the tyrosine kinase inhibitor axitinib is associated with increased glucose metabolism in pancreatic adenocarcinoma

Alterations in energy (glucose) metabolism are key events in the development and progression of cancer. In pancreatic adenocarcinoma (PDAC) cells, we investigated changes in glucose metabolism induced by resistance to the receptor tyrosine kinase inhibitor (RTKI) axitinib. Here, we show that human cell lines and mouse PDAC cell lines obtained from the spontaneous pancreatic cancer mouse model (Kras^G12DPdx1-cre) were sensitive to axitinib. The anti-proliferative effect was due to a G2/M block resulting in loss of 70–75% cell viability in the most sensitive PDAC cell line. However, a surviving sub-population showed a 2- to 3-fold increase in [C-14]deoxyglucose ([C-14]DG) uptake. This was sustained in axitinib-resistant cell lines, which were derived from parental PDAC. In addition to the axitinib-induced increase in [C-14]DG uptake, we observed a translocation of glucose transporter-1 (Glut-1) transporters from cytosolic pools to the cell surface membrane and a 2-fold increase in glycolysis rates measured by the extracellular acidification rate (ECAR). We demonstrated an axitinib-induced increase in phosphorylated Protein Kinase B (pAkt) and by blocking pAkt with a phosphatidylinositol-3 kinase (PI3K) inhibitor we reversed the Glut-1 translocation and restored sensitivity to axitinib treatment. Combination treatment with both axitinib and Akt inhibitor in parental pancreatic cell line resulted in a decrease in cell viability beyond that conferred by single therapy alone. Our study shows that PDAC resistance to axitinib results in increased glucose metabolism mediated by activated Akt. Combining axitinib and an Akt inhibitor may improve treatment in PDAC.