Inhibition of bacterial ice nucleators by fish antifreeze glycoproteins

Certain bacteria promote the formation of ice in super-cooled water by means of ice nucleators which contain a unique protein associated with the cell membrane. Ice nucleators in general are believed to act by mimicking the structure of an ice crystal surface, thus imposing an ice-like arrangement on the water molecules in contact with the nucleating surface and lowering the energy necessary for the initiation of ice formation. Quantitative investigation of the bacterial ice-nucleating process has recently been made possible by the discovery of certain bacteria that shed stable membrane vesicles with ice nucleating activity. The opposite effect, inhibition of ice formation, has been described for a group of glycoproteins found in different fish and insect species. This group of substances, termed antifreeze glycoproteins (AFGPs), promotes the supercooling of water with no appreciable effect on the equilibrium freezing point or melting temperature. Substantial evidence now indicates that AFGPs act by binding to a growing ice crystal and slowing crystal growth. As the ice-nucleating protein surface is believed to have a structure similar to an embryonic ice crystal, AFGPs might be predicted to interact directly with a bacterial ice-nucleating site. We report here that AFGPs from the antarctic fish Dissostichus mawsoni inhibit the ice-nucleating activity of membrane vesicles from the bacterium Erwinia herbicola. The inhibition effect shows saturation at high concentration of AFGP and conforms to a simple binding reaction between the AFGP and the nucleation centre.     

Inhibition of fading in fluorescence microscopy of fixed cells.

Following Hirschfeld et al., dithionite was added to mounting media to inhibit fluorescence fading. Excellent response is reported for fluorescein, acridine orange, 33258 Hoechst, acriflavine, berberine (and ethidium bromide), but not for quinacrine.     

Aneuploids in Pearl millet

Zusammenfassung Es wurden von der Nachkommenschaft triploider PerlhirsePennisetum typhoides (2n=14) aneuploide, das heisst einfach-trisome, zweifach-, dreifach- und tetrasome Pflanzen isoliert.     

Renewal of noradrenaline in different zones of the central nervous system of inbred mice strains and their recombinants]

A good correlation exists between the learning capacity and norepinephrine metabolism in the neocortex of C57 and Balb inbred Mice strains, as well as their F1 hybrids and seven recombinant inbred strains derived from their cross. The animals with a better learning performance are characterised by low levels of norepinephrine, as well as a slow metabolic rate of this neurotransmitter in the cortex. Such a correlation has not been found to exist in the other cerebral regions studied.     

Phospholipase Cgamma1 controls surface expression of TRPC3 through an intermolecular PH domain

Many ion channels are regulated by lipids, but prominent motifs for lipid binding have not been identified in most ion channels. Recently, we reported that phospholipase Cgamma1 (PLC-gamma1) binds to and regulates TRPC3 channels, components of agonist-induced Ca2+ entry into cells. This interaction requires a domain in PLC-gamma1 that includes a partial pleckstrin homology (PH) domain-a consensus lipid-binding and protein-binding sequence. We have developed a gestalt algorithm to detect hitherto 'invisible' PH and PH-like domains, and now report that the partial PH domain of PLC-gamma1 interacts with a complementary partial PH-like domain in TRPC3 to elicit lipid binding and cell-surface expression of TRPC3. Our findings imply a far greater abundance of PH domains than previously appreciated, and suggest that intermolecular PH-like domains represent a widespread signalling mode.     

Hereditary hypertension caused by chimaeric gene duplications and ectopic expression of aldosterone synthase.

Patients with glucocorticoid-remediable aldosteronism (GRA) from 12 kindreds possess chimaeric gene duplications arising from unequal crossing-over, fusing regulatory sequences of steroid 11 beta-hydroxylase to coding sequences of aldosterone synthase. These chimaeric genes are specific for GRA and explain the biochemistry, physiology and genetics of this form of hypertension. Sites of crossing over range from intron 2 to intron 4. Most mutations have arisen independently from either sister or non-sister chromatid exchange between these genes, which are only 45 kilobases apart. The possibility of a susceptibility allele for GRA of Irish origin is suggested. These findings indicate the utility of a direct genetic test for this disorder.     

Uncovering the Neoproterozoic carbon cycle

Interpretations of major climatic and biological events in Earth history are, in large part, derived from the stable carbon isotope records of carbonate rocks and sedimentary organic matter. Neoproterozoic carbonate records contain unusual and large negative isotopic anomalies within long periods (10-100 million years) characterized by δ(13)C in carbonate (δ(13)C(carb)) enriched to more than +5 per mil. Classically, δ(13)C(carb) is interpreted as a metric of the relative fraction of carbon buried as organic matter in marine sediments, which can be linked to oxygen accumulation through the stoichiometry of primary production. If a change in the isotopic composition of marine dissolved inorganic carbon is responsible for these excursions, it is expected that records of δ(13)C(carb) and δ(13)C in organic carbon (δ(13)C(org)) will covary, offset by the fractionation imparted by primary production. The documentation of several Neoproterozoic δ(13)C(carb) excursions that are decoupled from δ(13)C(org), however, indicates that other mechanisms may account for these excursions. Here we present δ(13)C data from Mongolia, northwest Canada and Namibia that capture multiple large-amplitude (over 10 per mil) negative carbon isotope anomalies, and use these data in a new quantitative mixing model to examine the behaviour of the Neoproterozoic carbon cycle. We find that carbonate and organic carbon isotope data from Mongolia and Canada are tightly coupled through multiple δ(13)C(carb) excursions, quantitatively ruling out previously suggested alternative explanations, such as diagenesis or the presence and terminal oxidation of a large marine dissolved organic carbon reservoir. Our data from Namibia, which do not record isotopic covariance, can be explained by simple mixing with a detrital flux of organic matter. We thus interpret δ(13)C(carb) anomalies as recording a primary perturbation to the surface carbon cycle. This interpretation requires the revisiting of models linking drastic isotope excursions to deep ocean oxygenation and the opening of environments capable of supporting animals.     

Microstructure and mechanical properties of AZ91 magnesium alloy subject to deep cryogenic treatments

AZ91 magnesium alloy was subjected to a deep cryogenic treatment. X-ray diffraction (XRD), scanning electronic microscopy (SEM), and transmission electronic microscopy (TEM) methods were utilized to characterize the composition and microstructure of the treated samples. The results show that after two cryogenic treatments, the quantity of the precipitate hardening β phase increases, and the sizes of the precipitates are refined from 8–10 μm to 2–4 μm. This is expected to be due to the decreased solubility of aluminum in the matrix at low temperature and the significant plastic deformation owing to internal differences in thermal contraction between phases and grains. The polycrystalline matrix is also noticeably refined, with the sizes of the subsequent nanocrystalline grains in the range of 50–100 nm. High density dislocations are observed to pile up at the grain boundaries, inducing the dynamic recrystallization of the microstructure, leading to the generation of a nanocrystalline grain structure. After two deep cryogenic treatments, the tensile strength and elongation are found to be substantially increased, rising from 243 MPa and 4.4% of as-cast state to 299 MPa and 5.1%.     

Transfer of a beta-turn structure to a new protein context

Four-residue beta-turns and larger loop structures represent a significant fraction of globular protein surfaces and play an important role in determining the conformation and specificity of enzyme active sites and antibody-combining sites. Turns are an attractive starting point to develop protein design methods, as they involve a small number of consecutive residues, adopt a limited number of defined conformations and are minimally constrained by packing interactions with the remainder of the protein. The ability to substitute one beta-turn geometry for another will extend protein engineering beyond the redecoration of fixed backbone conformations to include local restructuring and the repositioning of surface side chains. To determine the feasibility and to examine the effect of such a structural modification on the fold and thermodynamic stability of a globular protein, we have substituted a five-residue turn sequence from concanavalin A for a type I' beta-turn in staphylococcal nuclease. The resulting hybrid protein is folded and has full nuclease enzymatic activity but reduced thermodynamic stability. The crystal structure of the hybrid protein reveals that the guest turn sequence retains the conformation of the parent concanavalin A structure when substituted in the nuclease host.