Elastic constants of polymer-grafted lipid membranes

The surface expansion that is induced by the lateral pressure in the brush region of lipid membranes containing grafted polymers is deduced from the scaling and mean-field theories for the polymer brush, together with the equation of state for a lipid monolayer at the equivalence pressure with fluid lipid bilayers. Depending on the length and mole fraction of the polymer lipid, the membrane expansion can be appreciable. Direct experimental evidence for this lateral expansion comes from recent spin-label measurements with lipid membranes containing poly(ethylene glycol)-grafted lipids. The expansion in lipid area modifies the elastic constants of the polymer-grafted membranes in a way that opposes the direct elastic response of the polymer itself. Calculations as a function of polymer lipid content indicate that the net change in isothermal area expansion modulus of the membrane is negative but small, in contrast to previous predictions. A similar situation applies to the curvature elastic moduli of membranes containing short polymer lipids. For longer polymer lipids, however, the direct contribution of the polymer brush to the bending elastic constants dominates, and the increase in bending moduli with increasing polymer lipid content rapidly exceeds the basal values of the bare lipid membrane. The spontaneous (or intrinsic) curvature of the component monolayer of polymer lipid-containing membranes is calculated for the first time. The polymer brush contribution to spontaneous curvature scales quadratically with the polymer length, and at least quadratically with the mole fraction of polymer lipid.     

Specific spin labelling of the sugar-H(+) symporter, GalP, in cell membranes of Escherichia coli: site mobility and overall rotational diffusion of the protein

The D-galactose-H(+) symport protein (GalP) of Escherichia coli is a homologue of the human glucose transport protein, GLUT1. After amplified expression of the GalP transporter in E. coli, other membrane proteins were prereacted with N-ethylmaleimide in the presence of excess D-galactose to protect GalP. Inner membranes were then specifically spin labelled on Cys(374) of GalP with 4-maleimide-2,2,6,6-tetramethylpiperidine-1-oxyl. The electron paramagnetic resonance (EPR) spectra are characteristic of a single labelling site in which the mobility of the spin label is very highly constrained. This is confirmed with other nitroxyl spin labels, which are derivatives of iodoacetamide and indanedione. Saturation transfer EPR spectra indicate that the overall rotation of the GalP protein in the membrane is slow at low temperatures (approx. 2 degrees C), but considerably more rapid and highly anisotropic at physiological temperatures. The rate of rotation about the membrane normal at 37 degrees C is consistent with predictions for a 12-transmembrane helix assembly that is less than closely packed.     

Immunity to non-cerebral severe malaria is acquired after one or two infections

In areas of stable transmission, clinical immunity to mild malaria is acquired slowly, so it is not usually effective until early adolescence. Life-threatening disease is, however, restricted to a much younger age group, indicating that resistance to the severe clinical consequences of infection is acquired more quickly. Understanding how rapidly immunity develops to severe malaria is essential, as severe malaria should be the primary target of intervention strategies, and predicting the result of interventions that reduce host exposure will require consideration of these dynamics. Severe disease in childhood is less frequent in areas where transmission is the greatest. One explanation for this is that infants experience increased exposure to infection while they are protected from disease, possibly by maternal antibody. They therefore emerge from this period of clinical protection with considerably more immunity than those who experience lower transmission intensities. Here we use this data, assuming a period of clinical protection, to estimate the number of prior infections needed to reduce the risk of severe disease to negligible levels. Contrary to expectations, one or two successful infective bites seem to be all that is necessary across a broad range of transmission intensities.     

N-Acetyl Aspartic Acid (NAA) and N-Acetyl Aspartylglutamic Acid (NAAG) in Human Ventricular,Subarachnoid, and Lumbar Cerebrospinal Fluid

N-Acetylaspartic and N-acetylaspartylglutamic acid concentrations in human ventricular, subarachnoid and lumbar cerebrospinal fluid were measured by combined gas chromatography-mass spectrometry using selected ion monitoring with deuterated internal standards. N-Acetylaspartate concentrations were in the range 55, 9, and 1 M, respectively; N-acetylaspartylglutamate concentrations in the same fluids were in the range 8, 3 and 4 M, respectively. There did not appear to be any difference in lumbar fluid concentrations of either compound between control subjects, schizophrenic patients, Alzheimer's disease patients and a pooled group of patients with neurological degeneration. Ventricular concentrations of both compounds were greatly increased in deceased patients suggesting that maintenance of their intracellular concentrations is probably energy dependent. The concentrations of these compounds in lumbar cerebrospinal fluid from living, and ventricular cerebrospinal fluid from deceased subjects were weakly correlated with one another. In lumbar fluid neither compound appeared to be correlated with age. Analysis of serially collected lumbar samples from two subjects showed a weak concentration gradient for both compounds. Neither antipsychotic medication nor the acid transport inhibitor probenecid had any effect on lumbar concentrations of either compound. Attempts to use anion exchange high pressure liquid chromatography with UV detection for measurement of the low concentrations of N-acetylaspartate found in cerebrospinal fluid from living subjects were unsuccessful.     

Protection against atherosclerosis by estrogen is independent of plasma cholesterol levels in LDL receptor-deficient mice

Low density lipoprotein (LDL) receptor-deficient (LDLR-/-) mice consuming a high fat diet were used to assess the effect of endogenous and exogenous estradiol (E2) on atherosclerosis. Sexually mature female mice were ovariectomized (OVX) and implanted with subcutaneous, slow-release pellets designed to release 6 microg/day of exogenous 17beta-estradiol (17beta-E2 ), 17alpha-estradiol (17alpha-E2 ), or placebo (E2- deficient). Sham-operated control female (endogenous E2 ) and male mice were studied as controls. Aortic atherosclerotic lesion area was reduced by physiologic amounts of both endogenous and exogenous E2 compared to E2-deficient female mice. Although plasma cholesterol levels were reduced by exogenous E2 despite the absence of the LDL receptor, endogenous E2 was not associated with any cholesterol changes. In contrast, only 17alpha-E2 was associated with decreased fasting triglyceride. In subgroup analyses matched for time-averaged plasma total cholesterol, aortic lesion area was reduced by the presence of estradiol (E2 ). E2 protected LDLR-/- female mice from atherosclerosis and this protection was independent of changes in plasma cholesterol levels.     

Identification of uronic acid oxidase in plant peroxidase preparations

Commercial plant peroxidase preparations contained a uronic acid oxidase, separable from the peroxidase activity by ion exchange chromatography. The partially purified enzyme, devoid of peroxidase, oxidized hexuronic acids, with the greatest activity for D-glucuronic acid, whereas other aldoses were not substrates. The immediate products of reaction of D-glucuronic acid with oxygen were hydrogen peroxide and a D-glucarolactone, which was a very strong inhibitor of β-glucuronidase and believed to be the 1,5-lactone. The sensitivity to sulphite inhibition suggests that the enzyme is a flavoprotein.     

The C-terminal C1 cassette of the N -methyl-D-aspartate receptor 1 subunit contains a bi-partite nuclear localization sequence

The N -methyl-D-aspartate receptor (NMDAR) is a multimeric transmembrane protein composed of at least two subunits. One subunit, NR1, is derived from a single gene and can be subdivided into three regions: the N-terminal extracellular domain, the transmembrane regions, and the C-terminal intracellular domain. The N-terminal domain is responsible for Mg2+ metal ion binding and channel activity, while the transmembrane domains are important for ion channel formation. The intracellular C-terminal domain is involved in regulating receptor activity and subcellular localization. Our recent experiments indicated that the intracellular C-terminal domain, when expressed independently, localizes almost exclusively in the nucleus. An examination of the amino acid sequence reveals the presence of a putative nuclear localization sequence (NLS) in the C1 cassette of the NR1 intracellular C-terminus. Using an expression vector designed to test whether a putative NLS sequence is a valid, functional NLS, we have demonstrated that a bi-partite NLS does in fact exist within the NR1-1 C-terminus. Computer algorithms identified a putative helix-loop-helix motif that spanned the C0C1 cassettes of the C-terminus. These data suggest that the NR1 subunit may represent another member of a family of transmembrane proteins that undergo intramembrane proteolysis, releasing a cytosolic peptide that is actively translocated to the nucleus leading to alterations in gene regulation.     

The involvement of sodium and calcium ions in the release of amino acid neurotransmitters from mouse cortical slices elicited by hyperforin

Hyperforin is currently considered to be the major active antidepressant constituent of the medicinal herb St. John's wort (Hypericum perforatum L.). The mechanism of action however, is still largely unknown, although the involvement of sodium and calcium has been recently inferred. In the present study hyperforin (5 microM) significantly potentiated the release of endogenous aspartate and glutamate from mouse cortical slices when stimulated by veratridine or potassium. Hyperforin (5 microM) also stimulated the release of aspartate, glutamate, serine, glycine and GABA when perfused on its own. Perfusion of the sodium channel blocker, tetrodotoxin (TTX) inhibited the effect of hyperforin, whereas removal of extracellular calcium potentiated the effect. Our observations suggests that hyperforin increases the overflow of neurotransmitters from mouse cerebral cortex possibly through facilitating the entry of sodium into the neurone which leads to the release of calcium from intracellular stores.