The molecular structure and physical properties of elastin fibers as revealed by Raman microspectroscopy

Raman microspectroscopy has been used to investigate the structure of alpha-elastin and fibrous elastin from ligament and aorta, and to explore changes associated with mechanical strain and temperature. Although no vibrational modes associated with cross-linking of the fibers could be identified, the secondary structure of dehydrated fibrous elastin was significantly different from alpha-elastin. The former differed from previous experimental measurements, but was close to the theoretical predictions with 36% beta-structures, 46% unordered, and 18% alpha-helix. alpha-Elastin contained 29% beta-structures, 53% unordered, and 18% alpha-helix. In nuchal fibers the amide I mode was polarized, consistent with the peptide bond. Strains of up to 60% in ligament fiber bundles resulted in no significant shifts in peak position or in secondary structure. Polarization measurements revealed that the peptide bonds and several side chains re-orientated closer to the fiber axis. Heating nuchal fibers to 60 degrees C to increase the energetic component of the elasticity was associated with a 30% increase in the proportion of beta-structures in the amide I band, a 50% increase in the amide III band, and a 50% reduction in the signal from bound water. (c) 2008 Wiley Periodicals, Inc. Biopolymers 89: 931-940, 2008.This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com.     

Engineering poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer composition in E. coli

A strain of Escherichia coli was metabolically engineered to produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) of specified composition between 5% and 18% HV. A gene encoding propionyl-CoA synthetase (prpE from S. enterica) was placed under the control of the IPTG-inducible tac promoter (P(taclacUV5)) while the polyhydroxyalkanoate synthesis operon (phaBCA) from R. eutropha was expressed constitutively. A strain of E. coli harboring both plasmids was grown in defined medium and PHBV was produced with specified hydroxyvalerate (HV) molar content between 5% and 18%. The molecular weight of the copolymer was approximately 700,000 across various HV contents, and average polydispersity was approximately 1.3. The majority of the PHBV production occurred during the late exponential/stationary phase. The HV content of the copolymer generally peaked early in the incubation before falling to its final value. We found that the time profiles of PrpE activity, propionyl-CoA, and acetyl-CoA were well correlated to the HV content time profile. Despite an abundance of propionyl-CoA, incorporation of HV into the copolymer was inefficient. Therefore, both the PHA operon and conditions affecting the availability of propionyl-CoA must be chosen carefully to achieve the desired HV content. The ability to engineer copolymer composition control into an E. coli strain would be useful in cases where the feedstock composition is not adjustable.     

The impact of baseline diameter on flow-mediated dilation differs in young and older humans

Flow-mediated dilation (FMD) has become a commonly applied approach for the assessment of vascular function and health, but methods used to calculate FMD differ between studies. For example, the baseline diameter used as a benchmark is sometimes assessed before cuff inflation, whereas others use the diameter during cuff inflation. Therefore, we compared the brachial artery diameter before and during cuff inflation and calculated the resulting FMD in healthy children (n=45; 10+/-1 yr), adults (n=31; 28+/-6 yr), and older subjects (n=22; 58+/-5 yr). Brachial artery FMD was examined after 5 min of distal ischemia. Diameter was determined from either 30 s before cuff inflation or from the last 30 s during cuff inflation. Edge detection and wall tracking of high resolution B-mode arterial ultrasound images was used to calculate conduit artery diameter. Brachial artery diameter during cuff inflation was significantly larger than before inflation in children (P=0.02) and adults (P<0.001) but not in older subjects (P=0.59). Accordingly, FMD values significantly differed in children (11.2+/-5.1% vs. 9.4+/-5.2%; P=0.02) and adults (7.3+/-3.2% vs. 4.6+/-3.3%; P<0.001) but not in older subjects (6.3+/-3.4% vs. 6.0+/-4.2%; P=0.77). When the diameter before cuff inflation was used, an age-dependent decline was evident in FMD, whereas FMD calculated using the diameter during inflation was associated with higher FMD values in older than younger adults. In summary, the inflation of the cuff significantly increases brachial artery diameter, which results in a lower FMD response. This effect was found to be age dependent, which emphasizes the importance of using appropriate methodology to calculate the FMD.     

Liver fat, visceral adiposity, and sleep disturbances contribute to the development of insulin resistance and glucose intolerance in nondiabetic dialysis patients

Hemodialysis patients exhibit insulin resistance (IR) in target organs such as liver, muscles, and adipose tissue. The aim of this study was to identify contributors to IR and to develop a model for predicting glucose intolerance in nondiabetic hemodialysis patients. After a 2-h, 75-g oral glucose tolerance test (OGTT), 34 hemodialysis patients were divided into groups with normal (NGT) and impaired glucose tolerance (IGT). Indices of insulin sensitivity were derived from OGTT data. Measurements included liver and muscle fat infiltration and central adiposity by computed tomography scans, body composition by dual energy X-ray absorptiometer, sleep quality by full polysomnography, and functional capacity and quality of life (QoL) by a battery of exercise tests and questionnaires. Cut-off points, as well as sensitivity and specificity calculations were based on IR (insulin sensitivity index by Matsuda) using a receiver operator characteristics (ROC) curve analysis. Fifteen patients were assigned to the IGT, and 19 subjects to the NGT group. Intrahepatic fat content and visceral adiposity were significantly higher in the IGT group. IR indices strongly correlated with sleep disturbances, visceral adiposity, functional capacity, and QoL. Visceral adiposity, O2 desaturation during sleep, intrahepatic fat content, and QoL score fitted into the model for predicting glucose intolerance. A ROC curve analysis identified an intrahepatic fat content of > 3.97% (sensitivity, 100; specificity, 35.7) as the best cutoff point for predicting IR. Visceral and intrahepatic fat content, as well as QoL and sleep seemed to be involved at some point in the development of glucose intolerance in hemodialysis patients. Means of reducing fat depots in the liver and splachnic area might prove promising in combating IR and cardiovascular risk in hemodialysis patients.     

The American brine shrimp as an exotic invasive species in the western Mediterranean

The hypersaline environments and salterns present in the western Mediterranean region (including Italy, southern France, the Iberian Peninsula and Morocco) contain autochthonous forms of the brine shrimp Artemia, with parthenogenetic diploid and tetraploid strains coexisting with the bisexual species A. salina. Introduced populations of the American brine shrimp A. franciscana have also been recorded in these Mediterranean environments since the 1980s. Based on brine shrimp cyst samples collected in these countries from 1980 until 2002, we were able to establish the present distribution of autochthonous brine shrimps and of A. franciscana, which is shown to be an expanding invasive species. The results obtained show that A. franciscana is now the dominant Artemia species in Portuguese salterns, along the French Mediterranean coast and in Cadiz bay (Spain). Co-occurrence of autochthonous (parthenogenetic) and American brine shrimp populations was observed in Morocco (Mar Chica) and France (Aigues Mortes), whereas A. franciscana was not found in Italian cyst samples. The results suggest these exotic A. franciscana populations originate as intentional or non-intentional inoculations through aquacultural (hatchery effluents) or pet market activities, and suggest that the native species can be rapidly replaced by the exotic species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Land-use trends in Endemic Bird Areas: global expansion of agriculture in areas of high conservation value

The impacts of humans on biodiversity tend to be exacerbated by the coincidence of human settlement with areas of high biological value, as demonstrated by regional, continental and global analyses. We present a global analysis, intersecting Endemic Bird Areas (EBAs) with fine‐scale data on changes in agricultural land use for the past 300 years and for four scenarios projecting land use up to 2050. The proportion of land in agricultural use is currently greater in EBAs than in the rest of the world (42.0% vs. 37.0%, respectively), has been historically (in 1700: 9.1% vs. 5.7%, through to 1900: 43.4% vs. 32.1%) and looks set to remain so in the future (44.6–56.1% vs. 37.0–43.2%; depending on scenario). However, the future course of agricultural expansion is more scenario‐dependent in EBAs than in the rest of the world, indicating that development policies have considerable potential to either ease or exacerbate the disproportionate impact of agriculture on areas of highest biological value.     

Helophyte germination in a Mediterranean salt marsh: Gut‐passage by ducks changes seed response to salinity

Question: In seeds which are regularly consumed by waterbirds in the field, how does gut‐passage modify their response to salinity gradients? Location: Doñana National Park salt marsh, south‐west of Spain. Methods: Seeds of Scirpus litoralis and Scirpus maritimus were collected and force fed to mallards (Anas platyrhynchos). Both the ingested seeds (passage) and non‐ingested seeds (controls) were exposed, in germination chambers, to a salinity range similar to that observed in the field (0–32 dS/m). After 30 days, the total percentage germination, the duration of the dormancy period and the germination speed were computed. The response of the different germination parameters to ingestion and salinity was analyzed using generalized lineal models. Recovery tests on seeds that did not germinate in the various treatments and tests of the effect of ingestion on the intrinsic variability in seed response were also performed. Results: An increase in salinity reduced germinability and increased the length of dormancy, while gut pas sage increased the intrinsic variability of the temporal seed response in both species. In S. litoralis there was a significant interaction between the effects of salinity and passage on germination rate. Passage increased germination rate at low salinities (≤2 dS/m) but decreased it at high salinities (≥4 dS/m). Conclusion: Gut‐passage by ducks significantly changes seed response to salinity. The outcome of plant‐animal interactions can be influenced by environmental gradients. Studies of germination in response to gut passage that do not take such gradients into account may produce misleading results.