Discovery of new A- and B-type laxaphycins with synergistic anticancer activity

Two new cyclic lipopeptides termed laxaphycins B4 (1) and A2 (2) were discovered from a collection of the marine cyanobacterium Hormothamnion enteromorphoides, along with the known compound laxaphycin A. The planar structures were solved based on a combined interpretation of 1D and 2D NMR data and mass spectral data. The absolute configurations of the subunits were determined by chiral LC-MS analysis of the hydrolysates, advanced Marfey’s analysis and 1D and 2D ROESY experiments. Consistent with similar findings on other laxaphycin A- and B-type peptides, laxaphycin B4 (1) showed antiproliferative effects against human colon cancer HCT116 cells with IC₅₀ of 1.7?µM, while laxaphycins A and A2 (2) exhibited weak activities. The two major compounds isolated from the sample, laxaphycins A and B4, were shown to act synergistically to inhibit the growth of HCT116 colorectal cancer cells.     

Hen harrier Circus cyaneus nest sites on the Isle of Mull are associated with habitat mosaics and constrained by topography

Capsule: Hen Harriers Circus cyaneus on the Isle of Mull, UK, are associated with habitat mosaics consisting of moorland, scrub and forestry but avoid grazed land, suggesting that forested habitats could be managed sympathetically for the Hen Harrier in the future should the current UK population increase.

Aims: To use distribution modelling to investigate nesting habitat associations using a long-term data set for the Hen Harrier on Mull.

Methods: We develop area-interaction models using a least absolute shrinkage and selection operator penalty to explore the distribution of 102 Hen Harrier nest sites in relation to habitat and topography. Our model is then successfully validated in tests using data for 70 nest sites from subsequent years.

Results: Our model is effective in predicting suitable areas for Hen Harrier nest sites and indicates that Hen Harriers on Mull are found in habitat mosaics below 200 m above sea level. Hen Harrier nest intensity is positively associated with increasing proportions of moorland and scrub, open canopy forestry and closed canopy forestry. Nest intensity is negatively associated with increasing proportions of grazed land.

Conclusion: Hen Harriers avoid grazed areas but are relatively tolerant of other habitat combinations. These findings are supported by previous observations of Hen Harrier habitat use and have implications for the recovery of some Hen Harrier populations in Special Protection Areas and future forest management. Open canopy forest and forest mosaics could potentially be incorporated into landscape-scale conservation plans for Hen Harriers using the population on Mull as an example.     

Determination of the Structure of the Catabolic N-Succinylornithine Transaminase (AstC) from Escherichia coli

Escherichia coli possesses two acyl ornithine aminotransferases, one catabolic (AstC) and the other anabolic (ArgD), that participate in L-arginine metabolism. Although only 58% identical, the enzymes have been shown to be functionally interchangeable. Here we have purified AstC and have obtained X-ray crystal structures of apo and holo-AstC and of the enzyme complexed with its physiological substrate, succinylornithine. We compare the structures obtained in this study with those of ArgD from Salmonella typhimurium obtained elsewhere, finding several notable differences. Docking studies were used to explore the docking modes of several substrates (ornithine, succinylornithine and acetylornithine) and the co-substrate glutamate/α-ketogluterate. The docking studies support our observations that AstC has a strong preference for acylated ornithine species over ornithine itself, and suggest that the increase in specificity associated with acylation is caused by steric and desolvation effects rather than specific interactions between the substrate and enzyme.     

Prebiotic synthesis of diaminopyrimidine and thiocytosine

The reaction of guanidine hydrochloride with cyanoacetaldehyde gives high yields (40–85%) of 2,4-diaminopyrimidine under the concentrated conditions of a drying lagoon model of prebiotic synthesis, in contrast to the low yields previously obtained under more dilute conditions. The prebiotic source of cyanoacetaldehyde, cyanoacetylene, is produced from electric discharges under reducing conditions. The effect of pH and concentration of guanidine hydrochloride on the rate of synthesis and yield of diaminopyrimidine were investigated, as well as the hydrolysis of diaminopyrimidine to cytosine, isocytosine, and uracil. Thiourea also reacts with cyanoacetaldehyde to give 2-thiocytosine, but the pyrimidine yields are much lower than with guanidine hydrochloride or urea. Thiocytosine hydrolyzes to thiouracil and cytosine and then to uracil. This synthesis would have been a significant prebiotic source of 2-thiopyrimidines and 5-substituted derivatives of thiouracil, many of which occur in tRNA. The applicability of these results to the drying lagoon model of prebiotic synthesis was tested by dry-down experiments where dilute solutions of cyanoacetaldehyde, guanidine hydrochloride, and 0.5m NaCl were evaporated over varying periods of time. The yields of diaminopyrimidine varied from 1 to 7%. These results show that drying lagoons and beaches may have been major sites of prebiotic syntheses.     

The mating system and relative performance of selfed and outcrossed progeny in Arabis fecunda (Brassicaceae)

We estimated rates of self-fertilization and inbreeding depression in the hermaphroditic perennial Arabis fecunda. Crosses were made on mesh-bagged wild plants, yielding 12 plants producing self-, outcross-, and naturally fertilized seeds that were then grown in a greenhouse. Analysis of variance indicated aboveground dry weight at 160 days differed among pollination treatments, but mean seed weight, number of seeds per fruit, and days to germination did not. For dry weight, selfed progeny have 9.4% reduction and naturally pollinated progeny a 3.7% reduction compared to outcrossed progeny, suggesting a 39% selling rate in Arabis. Significant inbreeding depression and a mixed mating system are evidence that the deleterious effects of self-fertilization are maintained through high rates of mildly deleterious mutation. Significant maternal-parent-by-pollination-treatment interactions for mean seed weight and dry weight are consistent with inbreeding depression caused by deleterious recessives and varying past maternal inbreeding.     

Adenosine 5'-O-(3-thio)triphosphate (ATPgammaS) is a substrate for the nucleotide hydrolysis and RNA unwinding activities of eukaryotic translation initiation factor eIF4A

Whereas ATPgammaS is often considered a nonhydrolyzable substrate for ATPases, we present evidence that ATPgammaS is a good substrate for the RNA-stimulated nucleotide hydrolysis and RNA unwinding activities of eIF4A. In the presence of saturating single-stranded poly(U) RNA, eIF4A hydrolyzes ATPgammaS.Mg and ATP.Mg with similar steady-state parameters (KM(NTP.Mg) = 66 and 58 microM and kcat = 1.0 and 0.97 min(-1), respectively). ATPgammaS.Mg also supports catalysis of RNA unwinding within 10-fold of the rate supported by ATP.Mg. The identical steady-state rate parameters, in comparison with the expected difference in the intrinsic rate of hydrolysis for ATP and ATPgammaS, suggest a nonchemical rate-limiting step for nucleotide hydrolysis. These results raise caution concerning the assumption that ATPgammaS is a nonhydrolyzable ATP analog and underscore the utility of thio-substituted NTPs as mechanistic probes.