Crystal structure of a lipid G protein-coupled receptor     

Hanson MA  Roth CB  Jo E  Griffith MT  Scott FL  Reinhart G  Desale H  Clemons B  Cahalan SM  Schuerer SC  Sanna MG  Han GW  Kuhn P  Rosen H  Stevens RC 《Science (New York, N.Y.)》2012,335(6070):851-855

The lyso-phospholipid sphingosine 1-phosphate modulates lymphocyte trafficking, endothelial development and integrity, heart rate, and vascular tone and maturation by activating G protein-coupled sphingosine 1-phosphate receptors. Here, we present the crystal structure of the sphingosine 1-phosphate receptor 1 fused to T4-lysozyme (S1P(1)-T4L) in complex with an antagonist sphingolipid mimic. Extracellular access to the binding pocket is occluded by the amino terminus and extracellular loops of the receptor. Access is gained by ligands entering laterally between helices I and VII within the transmembrane region of the receptor. This structure, along with mutagenesis, agonist structure-activity relationship data, and modeling, provides a detailed view of the molecular recognition and requirement for hydrophobic volume that activates S1P(1), resulting in the modulation of immune and stromal cell responses.  相似文献   

Direct detection of projectile relics from the end of the lunar basin-forming epoch     

Joy KH  Zolensky ME  Nagashima K  Huss GR  Ross DK  McKay DS  Kring DA 《Science (New York, N.Y.)》2012,336(6087):1426-1429

The lunar surface, a key proxy for the early Earth, contains relics of asteroids and comets that have pummeled terrestrial planetary surfaces. Surviving fragments of projectiles in the lunar regolith provide a direct measure of the types and thus the sources of exogenous material delivered to the Earth-Moon system. In ancient [>3.4 billion years ago (Ga)] regolith breccias from the Apollo 16 landing site, we located mineral and lithologic relics of magnesian chondrules from chondritic impactors. These ancient impactor fragments are not nearly as diverse as those found in younger (3.4 Ga to today) regolith breccias and soils from the Moon or that presently fall as meteorites to Earth. This suggests that primitive chondritic asteroids, originating from a similar source region, were common Earth-Moon-crossing impactors during the latter stages of the basin-forming epoch.  相似文献   

Arbuscular mycorrhizal fungi increase organic carbon decomposition under elevated CO2     

L Cheng  FL Booker  C Tu  KO Burkey  L Zhou  HD Shew  TW Rufty  S Hu 《Science (New York, N.Y.)》2012,337(6098):1084-1087

The extent to which terrestrial ecosystems can sequester carbon to mitigate climate change is a matter of debate. The stimulation of arbuscular mycorrhizal fungi (AMF) by elevated atmospheric carbon dioxide (CO(2)) has been assumed to be a major mechanism facilitating soil carbon sequestration by increasing carbon inputs to soil and by protecting organic carbon from decomposition via aggregation. We present evidence from four independent microcosm and field experiments demonstrating that CO(2) enhancement of AMF results in considerable soil carbon losses. Our findings challenge the assumption that AMF protect against degradation of organic carbon in soil and raise questions about the current prediction of terrestrial ecosystem carbon balance under future climate-change scenarios.  相似文献   

No straight path: roaming in both ground- and excited-state photolytic channels of NO3 → NO + O2     

Grubb MP  Warter ML  Xiao H  Maeda S  Morokuma K  North SW 《Science (New York, N.Y.)》2012,335(6072):1075-1078

Roaming mechanisms have recently been observed in several chemical reactions alongside trajectories that pass through a traditional transition state. Here, we demonstrate that the visible light-induced reaction NO(3) → NO + O(2) proceeds exclusively by roaming. High-level ab initio calculations predict specific NO Λ doublet propensities (orientations of the unpaired electron with respect to the molecular rotation plane) for this mechanism, which we discern experimentally by ion imaging. The data provide direct evidence for roaming pathways in two different electronic states, corresponding to both previously documented photolysis channels that produce NO + O(2). More broadly, the results raise intriguing questions about the overall prevalence of this unusual reaction mechanism.  相似文献   

Compartmentalized control of skin immunity by resident commensals     

S Naik  N Bouladoux  C Wilhelm  MJ Molloy  R Salcedo  W Kastenmuller  C Deming  M Quinones  L Koo  S Conlan  S Spencer  JA Hall  A Dzutsev  H Kong  DJ Campbell  G Trinchieri  JA Segre  Y Belkaid 《Science (New York, N.Y.)》2012,337(6098):1115-1119

Intestinal commensal bacteria induce protective and regulatory responses that maintain host-microbial mutualism. However, the contribution of tissue-resident commensals to immunity and inflammation at other barrier sites has not been addressed. We found that in mice, the skin microbiota have an autonomous role in controlling the local inflammatory milieu and tuning resident T lymphocyte function. Protective immunity to a cutaneous pathogen was found to be critically dependent on the skin microbiota but not the gut microbiota. Furthermore, skin commensals tuned the function of local T cells in a manner dependent on signaling downstream of the interleukin-1 receptor. These findings underscore the importance of the microbiota as a distinctive feature of tissue compartmentalization, and provide insight into mechanisms of immune system regulation by resident commensal niches in health and disease.  相似文献   

A long-lived lunar core dynamo     

Shea EK  Weiss BP  Cassata WS  Shuster DL  Tikoo SM  Gattacceca J  Grove TL  Fuller MD 《Science (New York, N.Y.)》2012,335(6067):453-456

Paleomagnetic measurements indicate that a core dynamo probably existed on the Moon 4.2 billion years ago. However, the subsequent history of the lunar core dynamo is unknown. Here we report paleomagnetic, petrologic, and (40)Ar/(39)Ar thermochronometry measurements on the 3.7-billion-year-old mare basalt sample 10020. This sample contains a high-coercivity magnetization acquired in a stable field of at least ~12 microteslas. These data extend the known lifetime of the lunar dynamo by 500 million years. Such a long-lived lunar dynamo probably required a power source other than thermochemical convection from secular cooling of the lunar interior. The inferred strong intensity of the lunar paleofield presents a challenge to current dynamo theory.  相似文献   

Public health and biosecurity. Adaptations of avian flu virus are a cause for concern     

Berns KI  Casadevall A  Cohen ML  Ehrlich SA  Enquist LW  Fitch JP  Franz DR  Fraser-Liggett CM  Grant CM  Imperiale MJ  Kanabrocki J  Keim PS  Lemon SM  Levy SB  Lumpkin JR  Miller JF  Murch R  Nance ME  Osterholm MT  Relman DA  Roth JA  Vidaver AK 《Science (New York, N.Y.)》2012,335(6069):660-661

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Structural biology. How a neurotoxin survives     

Adler M 《Science (New York, N.Y.)》2012,335(6071):928-929

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Evidence for the involvement of Aphanomyces cochlioides and Pythium spp. in ‘girth scab’ disease of sugar beet in Bavaria     

Nechwatal  Jan  Leiminger  Jürgen  Poschenrieder  Georg  Zellner  Michael 《植物病害和植物保护杂志》2012,119(3):85-91

Journal of Plant Diseases and Protection - The term ‘girth scab’ describes a chronic disease of sugar beet roots (Beta vulgaris ssp. vulgaris) for which the causes still remain unclear....  相似文献   

Comment on "Nonreciprocal light propagation in a silicon photonic circuit"     

Fan S  Baets R  Petrov A  Yu Z  Joannopoulos JD  Freude W  Melloni A  Popović M  Vanwolleghem M  Jalas D  Eich M  Krause M  Renner H  Brinkmeyer E  Doerr CR 《Science (New York, N.Y.)》2012,335(6064):38; author reply 38

We show that the structure demonstrated by Feng et al. (Reports, 5 August 2011, p. 729) cannot enable optical isolation because it possesses a symmetric scattering matrix. Moreover, one cannot construct an optical isolator by incorporating this structure into any system as long as the system is linear and time-independent and is described by materials with a scalar dielectric function.  相似文献