The influence of dolichols on fluidity of mouse synaptic plasma membranes

Dolichols are isoprenologues which constitute an important component of biological membranes. However, an understanding of the effects of dolichols on the organization and dynamics of biological membranes has not been forthcoming. The experiments reported here are aimed at understanding the effects of dolichols on the physical properties of mouse brain synaptic plasma membranes. The effect of dolichols incorporated into mouse brain synaptic plasma membranes on fluorescent and electron spin resonance probes sensing the hydrophobic core differed from that of probes reporting closer to the surface of membrane bilayers. Dolichols significantly (P less than 0.01) lowered the polarization, limiting anisotropy, and order parameter of diphenylhexatriene in synaptic plasma membranes and liposomes extracted from synaptic plasma membranes, without changing the rotational relaxation time. Similarly, dolichol increased the fluidity reported by 16-doxylstearic acid in synaptic plasma membranes or liposomes extracted from synaptic plasma membranes. In contrast, dolichols exerted no effect on those properties for trans-parinaric acid or 5-doxylstearic acid in synaptic plasma membranes or liposomes derived therefrom. Dolichols can dramatically alter the structure and dynamics of lipid motion in synaptic plasma membranes and these effects are dependent on the location of the probe in the membrane.     

Photosynthesis and water relations and the role of anatomy in Umbilicariaceae (lichenes) from Central Spain

Summary The response of net photosynthesis and dark respiration in eight species of Umbilicariaceae (lichenes) to temperature (-5, 0, 5, 10, 15, 20, 25, 30°C) and irradiance (55, 110, 220, 400, 620 mol photons m^-2 s^-1 PAR) was studied. The samples were collected in montane and alpine localities of the Spanish Sistema Central. The species differed widely in their net photosynthetic rates. The optimal temperature for net photosynthesis in alpine species was significantly lower than in montane species. Montane species were more photophytic than alpine ones. Water saturation and water loss rate were dependent on morphology and particularly anatomy of the thallus. The physiological and structural data are useful in the interpretation of the ecology and altitudinal distribution of the Umbilicariaceae. No adaptation could be linked to particularities of the mediterranean climate.     

Dermatobia, the neotropical warble fly

The neotropical warble fly, Dermatobia hominis (Fig. 1), has plagued neotropical America since preColombian times, and has become an economically important pest causing substantial losses to the meat, milk and leather industries from northern Mexico down to northern Argentina. Its life cycle (Box 1) is astonishingly complex, requiring another insect as a phoretic carrier of its eggs to the skin of its mammal hosts. Here Eugenio Sancho discusses factors that contribute to the current economic and public health importance of this myiasis-causing fly.     

The involvement of histone H1[0] in chromatin structure.

Micrococcal nuclease digestion and light scattering are used to compare native chromatins with various histone H1[0] contents. The experimental data show that the higher the H1[0] content, the greater the ability to form compact structures with increasing ionic strength, and the lower the DNA accessibility to micrococcal nuclease. On the contrary, reconstituted samples from H1-depleted chromatin and pure individual H1 fractions behave in such a way that samples reconstituted with pure H1 degree give rise to a looser structure, more accessible to nuclease than samples reconstituted with H1-1. This contradiction suggests that the effect of H1o on chromatin structure must originate from the interaction of this histone with other components in native chromatin among which other histone H1 subfractions are good candidates.     

Acute and Chronic Effects of Ethanol on Transbilayer Membrane Domains

Alcohols, including ethanol, have a specific effect on transbilayer and lateral membrane domains. Recent evidence has shown that alcohols in vitro have a greater effect on fluidity of one leaflet as compared to the other. The present study examined effects of chronic ethanol consumption on fluidity of synaptic plasma membrane (SPM) exofacial and cytofacial leaflets using trinitrobenzenesulfonic acid (TNBS) labeling and differential polarized fluorometry of 1,6-diphenyl-1,3,5-hexatriene (DPH). Mice were administered ethanol or a control liquid diet for 3 weeks. Animals were killed and SPM prepared. The exofacial leaflet of SPM was significantly more fluid than the cytofacial leaflet in both groups, as indicated by limiting anisotropy of DPH. However, differences between the two leaflets were much smaller in the ethanol-treated group. Ethanol at concentrations seen clinically had a greater effect in vitro on the more fluid exofacial leaflet. This asymmetric effect of ethanol was significantly diminished in the exofacial leaflet of the ethanol-treated mice. Chronic ethanol consumption has a specific effect on membranes. Membrane functions that may be regulated by asymmetry of fluidity and lipid distribution may be altered by chronic ethanol consumption.     

Net nitrogen mineralization in soils under six indigenous tree species,an abandoned pasture and a secondary forest in the atlantic lowlands of costa rica

Nitrogen mineralization, nitrification potentials, pH, total N, C, extractable P and cations were measured in soils under 4-year-old, mono-specific stands of six fast-growing, native tree species, an abandoned pasture, and a 20-year-old secondary forest, as part of a study on the use of indigenous tree species for rehabilitation of soil fertility on degraded pastures at the La Selva Biological Station in the Atlantic humid lowlands of Costa Rica. Soil net nitrification potential rates were higher under two N-fixing, leguminous species,Stryphnodendron microstachyum Poepp. et Endl. (1.1–1.9 mg kg^–1 day^–1) andDalbergia tucurensis Donn. Smith (0.7–1.5 mg kg^–1 day^–1), than under the non-N-fixing trees in the plantation,Vochysia guatemalesis Don. Sm.,Vochysia ferruginea Mart,Dipteryx panamensis (Pittier) Record and Mell andHyeronima alchorneoides Fr. Allemao (0.2–0.8 mg kg^–1 day^–1). Values under the N-fixing trees were comparable to those found in secondary forest. There were no statistically significant differences in soil total N or in other nurtients between the species. Results of pH measurements done before and after incubation did not show any clear evidence of a pH drop attributable to nitrification.     

Conformational stability of apoflavodoxin.

Flavodoxins are alpha/beta proteins that mediate electron transfer reactions. The conformational stability of apoflavodoxin from Anaboena PCC 7119 has been studied by calorimetry and urea denaturation as a function of pH and ionic strength. At pH > 12, the protein is unfolded. Between pH 11 and pH 6, the apoprotein is folded properly as judged from near-ultraviolet (UV) circular dichroism (CD) and high-field 1H NMR spectra. In this pH interval, apoflavodoxin is a monomer and its unfolding by urea or temperature follows a simple two-state mechanism. The specific heat capacity of unfolding for this native conformation is unusually low. Near its isoelectric point (3.9), the protein is highly insoluble. At lower pH values (pH 3.5-2.0), apoflavodoxin adopts a conformation with the properties of a molten globule. Although apoflavodoxin at pH 2 unfolds cooperatively with urea in a reversible fashion and the fluorescence and far-UV CD unfolding curves coincide, the transition midpoint depends on the concentration of protein, ruling out a simple two-state process at acidic pH. Apoflavodoxin constitutes a promising system for the analysis of the stability and folding of alpha/beta proteins and for the study of the interaction between apoflavoproteins and their corresponding redox cofactors.     

Alpha-helix stability in proteins. I. Empirical correlations concerning substitution of side-chains at the N and C-caps and the replacement of alanine by glycine or serine at solvent-exposed surfaces.

The importance of amino acid side-chains in helix stability has been investigated by making a series of mutations at the N-caps, C-caps and internal positions of the solvent-exposed faces of the two alpha-helices of barnase. There is a strong positional and context dependence of the effect of a particular amino acid on stability. Correlations have been found that provide insight into the physical basis of helix stabilization. The relative effects of Ala and Gly (or Ser) may be rationalized on the basis of solvent-accessible surface areas: burial of hydrophobic surface stabilizes the protein as does exposure to solvent of unpaired hydrogen bond donors or acceptors in the protein. There is a good correlation between the relative stabilizing effects of Ala and Gly at internal positions with the total change in solvent-accessible hydrophobic surface area of the folded protein on mutation of Ala----Gly. The relationship may be extended to the N and C-caps by including an extra term in hydrophilic surface area for the solvent exposure of the non-intramolecularly hydrogen-bonded main-chain CO, NH or protein side-chain hydrogen bonding groups. The requirement for solvent exposure of the C-cap main-chain CO groups may account for the strong preference for residues having positive phi and psi angles at this position, since this alpha L-conformation results in the largest solvent exposure of the C-terminal CO groups. Glycine in an alpha L-conformation results in the greatest exposure of these CO groups. Further, the side-chains of His, Asn, Arg and Lys may, with positive phi and psi-angles, form a hydrogen bond with the backbone CO of residue in position C -3 (residues are numbered relative to the C-cap). The preferences at the C-cap are Gly much greater than His greater than Asn greater than Arg greater than Lys greater than Ala approximately Ser approximately greater than Asp. The preferences at the N-cap are determined by hydrogen bonding of side-chains or solvent to the exposed backbone NH groups and are: Thr approximately Asp approximately Ser greater than Gly approximately Asn greater than Gln approximately Glu approximately His greater than Ala greater than Val much greater than Pro. These general trends may be obscured when mutation allows another side-chain to become a surrogate cap.(ABSTRACT TRUNCATED AT 400 WORDS)     

Histidine-aromatic interactions in barnase. Elevation of histidine pKa and contribution to protein stability.

Aromatic side-chains are found in the vicinity of histidine residues in many proteins and protein complexes. We have studied the interaction between a histidine residue (His18) and aromatic residues at position 94 in barnase. Three different techniques have been applied to show that Trp94 interacts more strongly with the protonated form of His18. The aromatic-histidine interaction stabilizes the protonated form of histidine by 0.8 to 1 kcal mol-1 relative to the unprotonated and, thereby, increases its pKa value. This was shown indirectly from the pH dependence of the stability of the wild-type protein and the mutant Trp94----Leu; and directly from the difference in pKa of His18 between wild-type barnase and the same mutant protein, and from double-mutant cycles that measure the total interaction energy of Trp94 with His18 at both low and high pH. When Trp94 is replaced by other aromatic amino acids, the strength of the interaction decreases in the series His-Trp greater than His-Tyr greater than His-Phe. The interaction is not masked by high salt concentrations. The raising of the pKa value of His18 by interaction with Trp94 is shown to be consistent with solution studies with model compounds. The histidine-aromatic interaction could have implications in binding and catalysis for modulation of the histidine pKa value.