Rise and fall of species occupancy in Cenozoic fossil mollusks     

Foote M  Crampton JS  Beu AG  Marshall BA  Cooper RA  Maxwell PA  Matcham I 《Science (New York, N.Y.)》2007,318(5853):1131-1134

In the time between speciation and extinction, a species' ecological and biogeographic footprint-its occupancy-will vary in response to macroecological drivers and historical contingencies. Despite their importance for understanding macroecological processes, general patterns of long-term species occupancy remain largely unknown. We documented the occupancy histories of Cenozoic marine mollusks from New Zealand. For both genera and species, these show a distinct pattern of increase to relatively short-lived peak occupancy at mid-duration, followed by a decline toward extinction. Thus, species at greatest risk for extinction are those that have already been in decline for a substantial period of time. This pattern of protracted rise and fall stands in contrast to that of incumbency, insofar as species show no general tendency to stay near maximal occupancy once established.  相似文献   

Crystal structure of the malaria vaccine candidate apical membrane antigen 1     

Pizarro JC  Vulliez-Le Normand B  Chesne-Seck ML  Collins CR  Withers-Martinez C  Hackett F  Blackman MJ  Faber BW  Remarque EJ  Kocken CH  Thomas AW  Bentley GA 《Science (New York, N.Y.)》2005,308(5720):408-411

Apical membrane antigen 1 from Plasmodium is a leading malaria vaccine candidate. The protein is essential for host-cell invasion, but its molecular function is unknown. The crystal structure of the three domains comprising the ectoplasmic region of the antigen from P. vivax, solved at 1.8 angstrom resolution, shows that domains I and II belong to the PAN motif, which defines a superfamily of protein folds implicated in receptor binding. We also mapped the epitope of an invasion-inhibitory monoclonal antibody specific for the P. falciparum ortholog and modeled this to the structure. The location of the epitope and current knowledge on structure-function correlations for PAN domains together suggest a receptor-binding role during invasion in which domain II plays a critical part. These results are likely to aid vaccine and drug design.  相似文献   

The neural basis of economic decision-making in the Ultimatum Game     

Sanfey AG  Rilling JK  Aronson JA  Nystrom LE  Cohen JD 《Science (New York, N.Y.)》2003,300(5626):1755-1758

The nascent field of neuroeconomics seeks to ground economic decision making in the biological substrate of the brain. We used functional magnetic resonance imaging of Ultimatum Game players to investigate neural substrates of cognitive and emotional processes involved in economic decision-making. In this game, two players split a sum of money;one player proposes a division and the other can accept or reject this. We scanned players as they responded to fair and unfair proposals. Unfair offers elicited activity in brain areas related to both emotion (anterior insula) and cognition (dorsolateral prefrontal cortex). Further, significantly heightened activity in anterior insula for rejected unfair offers suggests an important role for emotions in decision-making.  相似文献   

Chemical emissions: an ongoing issue     

Lockwood AH 《Science (New York, N.Y.)》2002,298(5593):541-2; author reply 541-2

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Pinatubo eruption. The climatic aftermath     

Robock A 《Science (New York, N.Y.)》2002,295(5558):1242-1244

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Public health. A sound rationale needed for phase III HIV-1 vaccine trials     

Burton DR  Desrosiers RC  Doms RW  Feinberg MB  Gallo RC  Hahn B  Hoxie JA  Hunter E  Korber B  Landay A  Lederman MM  Lieberman J  McCune JM  Moore JP  Nathanson N  Picker L  Richman D  Rinaldo C  Stevenson M  Watkins DI  Wolinsky SM  Zack JA 《Science (New York, N.Y.)》2004,303(5656):316

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Proteoglycan-specific molecular switch for RPTPσ clustering and neuronal extension     

Coles CH  Shen Y  Tenney AP  Siebold C  Sutton GC  Lu W  Gallagher JT  Jones EY  Flanagan JG  Aricescu AR 《Science (New York, N.Y.)》2011,332(6028):484-488

Heparan and chondroitin sulfate proteoglycans (HSPGs and CSPGs, respectively) regulate numerous cell surface signaling events, with typically opposite effects on cell function. CSPGs inhibit nerve regeneration through receptor protein tyrosine phosphatase sigma (RPTPσ). Here we report that RPTPσ acts bimodally in sensory neuron extension, mediating CSPG inhibition and HSPG growth promotion. Crystallographic analyses of a shared HSPG-CSPG binding site reveal a conformational plasticity that can accommodate diverse glycosaminoglycans with comparable affinities. Heparan sulfate and analogs induced RPTPσ ectodomain oligomerization in solution, which was inhibited by chondroitin sulfate. RPTPσ and HSPGs colocalize in puncta on sensory neurons in culture, whereas CSPGs occupy the extracellular matrix. These results lead to a model where proteoglycans can exert opposing effects on neuronal extension by competing to control the oligomerization of a common receptor.  相似文献   

Fighting liverflukes with food safety education     

Ziegler AD  Andrews RH  Grundy-Warr C  Sithithaworn P  Petney TN 《Science (New York, N.Y.)》2011,331(6015):282-283

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Polar lightning and decadal-scale cloud variability on Jupiter     

Baines KH  Simon-Miller AA  Orton GS  Weaver HA  Lunsford A  Momary TW  Spencer J  Cheng AF  Reuter DC  Jennings DE  Gladstone GR  Moore J  Stern SA  Young LA  Throop H  Yanamandra-Fisher P  Fisher BM  Hora J  Ressler ME 《Science (New York, N.Y.)》2007,318(5848):226-229

Although lightning has been seen on other planets, including Jupiter, polar lightning has been known only on Earth. Optical observations from the New Horizons spacecraft have identified lightning at high latitudes above Jupiter up to 80 degrees N and 74 degrees S. Lightning rates and optical powers were similar at each pole, and the mean optical flux is comparable to that at nonpolar latitudes, which is consistent with the notion that internal heat is the main driver of convection. Both near-infrared and ground-based 5-micrometer thermal imagery reveal that cloud cover has thinned substantially since the 2000 Cassini flyby, particularly in the turbulent wake of the Great Red Spot and in the southern half of the equatorial region, demonstrating that vertical dynamical processes are time-varying on seasonal scales at mid- and low latitudes on Jupiter.  相似文献   

Effect of deamidation on stability for the collagen to gelatin transition     

Silva T  Kirkpatrick A  Brodsky B  Ramshaw JA 《Journal of agricultural and food chemistry》2005,53(20):7802-7806

Deamidation of amide residues, Asn and Gln, in collagen occurs during the manufacture of B-type gelatin and could affect the performance of B-type gelatins as it may affect the refolding of triple-helical junctional domains that are formed during gelation. Host-guest peptides of the form acetyl-(Gly-Pro-Hyp)3-Gly-Xaa-Yaa-(Gly-Pro-Hyp)4-Gly-Gly-amide, where the X- and Y-positions of the guest peptide are varied, have been used to examine the effect of changing Asn to Asp and Gln to Glu on triple-helix stability. This paper reports the stability of host-guest peptides containing the guest triplets Gly-Ala-Asn, Gly-Asn-Ala, Gly-Asn-Lys, Gly-Gln-Ala, Gly-Glu-Glu, and Gly-Leu-Glu. In combination with previous data, these now provide 15 pairs of peptides in which the effect of deamidation can be compared. These comparisons show that the deamidation of Asn to Asp, regardless of whether it occurred in either the X- or Y-position, always gave a stabilizing effect; deamidation of Gln in the X-position also led to an increase in stability. In contrast, deamidation of Gln in the Y-position was quite distinct, leading to destabilization. The higher observed frequency of Gln in the Y-position compared with other amides may account for the slight destabilization of collagen following deamidation.  相似文献