Phospholipid membrane protection by sugar molecules during dehydration - insights into molecular mechanisms using scattering techniques

Scattering techniques have played a key role in our understanding of the structure and function of phospholipid membranes. These techniques have been applied widely to study how different molecules (e.g., cholesterol) can affect phospholipid membrane structure. However, there has been much less attention paid to the effects of molecules that remain in the aqueous phase. One important example is the role played by small solutes, particularly sugars, in protecting phospholipid membranes during drying or slow freezing. In this paper, we present new results and a general methodology, which illustrate how contrast variation small angle neutron scattering (SANS) and synchrotron-based X-ray scattering (small angle (SAXS) and wide angle (WAXS)) can be used to quantitatively understand the interactions between solutes and phospholipids. Specifically, we show the assignment of lipid phases with synchrotron SAXS and explain how SANS reveals the exclusion of sugars from the aqueous region in the particular example of hexagonal II phases formed by phospholipids

Measurement of glucose exclusion from the fully hydrated DOPE inverse hexagonal phase

The degree of exclusion of glucose from the inverse hexagonal HII phase of fully hydrated DOPE is determined using contrast variation small angle neutron scattering and small angle X-ray scattering. The presence of glucose is found to favour the formation of the non-lamellar HII phase over the fluid lamellar phase, over a wide range of temperatures, while having no significant effect on the structure of the HII phase. Glucose is preferentially excluded from the lipid¿water interface resulting in a glucose concentration in the HII phase of less than half that in the coexisting aqueous phase. The degree of exclusion is quantified and the results are consistent with a hydration layer of pure water adjacent to the lipid head groups from which glucose is excluded. The osmotic gradient created by the difference in glucose concentration is determined and the influence of glucose on the phase behaviour of non-lamellar phase forming lipid systems is discussed

Measurement of glucose exclusion from the fully hydrated DOPE inverse hexagonal phase

The degree of exclusion of glucose from the inverse hexagonal HII phase of fully hydrated DOPE is determined using contrast variation small angle neutron scattering and small angle X-ray scattering. The presence of glucose is found to favour the formation of the non-lamellar HII phase over the fluid lamellar phase, over a wide range of temperatures, while having no significant effect on the structure of the HII phase. Glucose is preferentially excluded from the lipid-water interface resulting in a glucose concentration in the HII phase of less than half that in the coexisting aqueous phase. The degree of exclusion is quantified and the results are consistent with a hydration layer of pure water adjacent to the lipid head groups from which glucose is excluded. The osmotic gradient created by the difference in glucose concentration is determined and the influence of glucose on the phase behaviour of non-lamellar phase forming lipid systems is discussed

Downy Mildew of Sorghum. Information Bulletin no. 51

Downy mildew of sorghum (Peronosclerospora sorghi) is one of the most important diseases of sorghum and maize. It is distributed widely in Africa, Asia, and the Americas, where serious epidemics occur. Systemic infection causes complete or partial sterility of the panicle, resulting in yield loss roughly proportional to the disease incidence. The seriousness of the problem has resulted in significant investment to increase knowledge of the pathogen and to investigate various disease control measures. Several alternatives for the control of sorghum downy mildew are now available including cultural and chemical control, and the deployment of resistant varieties. The current state of knowledge of the pathogen's biology, epidemiology, variability, and control are described in this bulletin, together with practical aspects of disease management

Phylogenetic Study of Plant Q-type C2H2 Zinc Finger Proteins and Expression Analysis of Poplar Genes in Response to Osmotic, Cold and Mechanical Stresses

Plant Q-type C2H2 zinc finger transcription factors play an important role in plant tolerance to various environmental stresses such as drought, cold, osmotic stress, wounding and mechanical loading. To carry out an improved analysis of the specific role of each member of this subfamily in response to mechanical loading in poplar, we identified 16 two-fingered Q-type C2H2-predicted proteins from the poplar Phytozome database and compared their phylogenetic relationships with 152 two-fingered Q-type C2H2 protein sequences belonging to more than 50 species isolated from the NR protein database of NCBI. Phylogenetic analyses of these Q-type C2H2 proteins sequences classified them into two groups G1 and G2, and conserved motif distributions of interest were established. These two groups differed essentially in their signatures at the C-terminus of their two QALGGH DNA-binding domains. Two additional conserved motifs, MALEAL and LVDCHY, were found only in sequences from Group G1 or from Group G2, respectively. Functional significance of these phylogenetic divergences was assessed by studying transcript accumulation of six poplar C2H2 Q-type genes in responses to abiotic stresses; but no group specificity was found in any organ. Further expression analyses focused on PtaZFP1 and PtaZFP2, the two genes strongly induced by mechanical loading in poplars. The results revealed that these two genes were regulated by several signalling molecules including hydrogen peroxide and the phytohormone jasmonate

Differential response to resistance training in CHF according to ACE genotype

The Angiotensin Converting Enzyme (ACE) gene may influence the risk of heart disease and the response to various forms of exercise training may be at least partly dependent on the ACE genotype. We aimed to determine the effect of ACE genotype on the response to moderate intensity circuit resistance training in chronic heart failure (CHF) patients. Methods: The relationship between ACE genotype and the response to 11 weeks of resistance exercise training was determined in 37 CHF patients (New York Heart Association Functional Class=2.3±0.5; left ventricular ejection fraction 28±7%; age 64±12 years; 32:5 male:female) who were randomised to either resistance exercise (n=19) or inactive control group (n=18). Outcome measures included V˙ O2peak, peak power output and muscle strength and endurance. ACE genotype was determined using standard methods. Results: At baseline, patients who were homozygous for the I allele had higher V˙ O2peak (p=0.02) and peak power (p=0.003) compared to patients who were homozygous for the D allele. Patients with the D allele, who were randomised to resistance training, compared to non-exercising controls, had greater peak power increases (ID pb0.001; DD pb0.001) when compared with patients homozygous for the I allele, who did not improve. No significant genotype-dependent changes were observed in V˙ O2peak, muscle strength, muscle endurance or lactate threshold. Conclusion: ACE genotype may have a role in exercise tolerance in CHF and could also influence the effectiveness of resistance training in this condition

Reexamining the effect of gustatory disgust on moral judgment: A multi-lab direct replication of Eskine, Kacinik, and Prinz (2011)

Tufts University Faculty Research Awar

Direct Observation of Single Amyloid-β(1-40) Oligomers on Live Cells: Binding and Growth at Physiological Concentrations

Understanding how amyloid-β peptide interacts with living cells on a molecular level is critical to development of targeted treatments for Alzheimer's disease. Evidence that oligomeric Aβ interacts with neuronal cell membranes has been provided, but the mechanism by which membrane binding occurs and the exact stoichiometry of the neurotoxic aggregates remain elusive. Physiologically relevant experimentation is hindered by the high Aβ concentrations required for most biochemical analyses, the metastable nature of Aβ aggregates, and the complex variety of Aβ species present under physiological conditions. Here we use single molecule microscopy to overcome these challenges, presenting direct optical evidence that small Aβ(1-40) oligomers bind to living neuroblastoma cells at physiological Aβ concentrations. Single particle fluorescence intensity measurements indicate that cell-bound Aβ species range in size from monomers to hexamers and greater, with the majority of bound oligomers falling in the dimer-to-tetramer range. Furthermore, while low-molecular weight oligomeric species do form in solution, the membrane-bound oligomer size distribution is shifted towards larger aggregates, indicating either that bound Aβ oligomers can rapidly increase in size or that these oligomers cluster at specific sites on the membrane. Calcium indicator studies demonstrate that small oligomer binding at physiological concentrations induces only mild, sporadic calcium leakage. These findings support the hypothesis that small oligomers are the primary Aβ species that interact with neurons at physiological concentrations

Mechanisms Underlying the Confined Diffusion of Cholera Toxin B-Subunit in Intact Cell Membranes

Multivalent glycolipid binding toxins such as cholera toxin have the capacity to cluster glycolipids, a process thought to be important for their functional uptake into cells. In contrast to the highly dynamic properties of lipid probes and many lipid-anchored proteins, the B-subunit of cholera toxin (CTxB) diffuses extremely slowly when bound to its glycolipid receptor GM1 in the plasma membrane of living cells. In the current study, we used confocal FRAP to examine the origins of this slow diffusion of the CTxB/GM1 complex at the cell surface, relative to the behavior of a representative GPI-anchored protein, transmembrane protein, and fluorescent lipid analog. We show that the diffusion of CTxB is impeded by actin- and ATP-dependent processes, but is unaffected by caveolae. At physiological temperature, the diffusion of several cell surface markers is unchanged in the presence of CTxB, suggesting that binding of CTxB to membranes does not alter the organization of the plasma membrane in a way that influences the diffusion of other molecules. Furthermore, diffusion of the B-subunit of another glycolipid-binding toxin, Shiga toxin, is significantly faster than that of CTxB, indicating that the confined diffusion of CTxB is not a simple function of its ability to cluster glycolipids. By identifying underlying mechanisms that control CTxB dynamics at the cell surface, these findings help to delineate the fundamental properties of toxin-receptor complexes in intact cell membranes