Editors' Choice

Science  29 Nov 2019:
Vol. 366, Issue 6469, pp. 1091
  1. Drug Solvation

    A spoonful of sugar for your coffee

    1. Michael A. Funk

    Adding sugar to coffee can change the solubility and aggregation behavior of caffeine molecules.

    PHOTO: NEW AFRICA/SHUTTERSTOCK

    Although we brew coffee and tea in water, the psychoactive drug we crave, caffeine, is moderately hydrophobic and becomes more so as the temperature of a beverage decreases. Stacked aggregates of caffeine molecules, which may have different properties, can form at saturation. Shumilin et al. investigated the distribution of caffeine aggregates and monomers in response to increasing concentration of a common excipient: sugar. Although various sugars decreased overall caffeine solubility, they had a preferential effect on oligomers and resulted in a higher relative proportion of caffeine in the monomer form.

    J. Am. Chem. Soc. 141, 18056 (2019).

  2. Heart Disease

    Exercise finds its niche

    1. Paula A. Kiberstis

    Regular physical activity is associated with a lower rate of death from heart disease, but the underlying mechanisms are not fully understood. Frodermann et al. examined the effect of exercise on cardiovascular inflammation, a known risk factor for atherosclerosis, by studying mice that voluntarily ran for long distances on exercise wheels. They found that these physically active mice had fewer inflammatory cells (leukocytes) than sedentary mice, an effect they traced to diminished activity of hematopoietic stem and progenitor cells (HSPCs). The lower activity of HSPCs was due at least in part to exercise-induced reduction in the levels of leptin, a hormone produced by fat tissue that regulates cells within the hematopoietic bone marrow niche.

    Nat. Med. 25, 1761 (2019).

  3. Mutualism

    Root to shoot protection

    1. Caroline Ash

    Honey bee, Apis mellifera, feeding on a strawberry flower

    PHOTO: JESS311/ISTOCK.COM

    Noble rot caused by the gray mold Botrytis cinerea is essential to producing the world's finest wines, but under different conditions, this mold devastates soft fruit crops. Kim et al. investigated how plants and their microbial partners defend against this ubiquitous greenhouse pathogen. They identified a filamentous Streptomyces sp. bacterium, a genus renowned for synthesizing antibioticlike molecules, associated with strawberry plants. Streptomyces globisporus SP6C4 was found in all vascular tissues of the plants, even in the pollen. The occurrence of SP6C4 associated with low levels of mold disease. In greenhouse experiments, honey bees ingested the SP6C4-laden strawberry pollen and not only benefited from a reduction in potential insect pathogens but also acted as vectors of the protective SP6C4 to mold-susceptible greenhouse plants. The natural products produced by SP6C4 have not yet been characterized.

    Nat. Commun. 10, 4802 (2019).

  4. Cell Biology

    Prising open the human brain

    1. Stella M. Hurtley

    Meningococcus (Neisseria meningitidis) causes meningitis and rapidly progressing fatal shock, but only in humans. To invade the brain, meningococcus uses its filamentous pili to hijack the β2-adrenergic receptor (β2AR), inducing an allosteric β-arrestin–biased signaling cascade in endothelial cells lining the capillaries of the brain. This cascade allows bacterial colonies to tether to endothelial cells, despite the shear stress of blood flow, and also promotes opening of endothelial junctions, which allows bacteria to penetrate the brain. Virion et al. sought to understand how a G protein–coupled receptor is activated by bacterial type IV pili proteins to transduce a signaling cascade that normally needs a cognate ligand. They found that β2AR activation requires two asparagine-branched glycan chains with terminally exposed sialic acid residues. Meningococcus triggers receptor signaling by exerting mechanical forces on β2AR glycans with its retractable pili. Because human glycans are unusual in exposing sialic acid residues on their glycans, this mechanism may help explain the specificity of meningococcus to its human host.

    Nat. Commun. 10, 4752 (2019).

  5. Neuroscience

    How to assemble a glutamate receptor

    1. Peter Stern

    The biogenesis of the AMPA glutamate receptor, which mediates fast synaptic transmission in the central nervous system, is not understood. Using a variety of high-resolution techniques, as well as behavioral studies, Schwenk et al. identified the protein constituents of the production line in the endoplasmic reticulum that assembles functional AMPA receptors in the mammalian brain. These protein constituents help to generate tetrameric assemblies from monomers of pore-forming receptor subunits. Genetic deletion of the oligomerizing proteins profoundly altered AMPA receptor–mediated neurotransmission and synaptogenesis, abolished activity-driven plasticity, and severely impaired learning in mice.

    Neuron 10.1016/j.neuron.2019.08.033 (2019).

  6. Arctic Warming

    Snow job

    1. H. Jesse Smith

    What is the cause of the observed reduction of surface albedo in the Arctic since the early 1980s? This surface albedo reduction is thought to be a major reason that the Arctic has warmed at a rate two to three times greater than the global average. Zhang et al. show that reductions of terrestrial snow cover, snow cover fraction over sea ice, and sea ice extent are coequally responsible for the albedo decline and that the decrease in snow cover is primarily due to rising surface air temperatures. Soot deposition has not been an important factor in the albedo change.

    Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1915258116 (2019).

  7. Inorganic Chemistry

    Aluminum squared

    1. Jake Yeston

    Three-coordinate aluminum compounds are potent Lewis acids: They readily attract electron donors, binding them to form a saturated tetrahedral product. Ebner et al. now report that four-coordinate aluminum can act as a Lewis acid, too, so long as it's forced ahead of time into a square planar geometry. To attain this unusual bonding motif, they embedded an aluminum(III) ion within a macrocycle of four negatively charged pyrrole donors. In addition to binding tetrahydrofuran, this aluminum center accepted hydride and fluoride ligands.

    J. Am. Chem. Soc. 141, 18009 (2019).

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