Summary
Biodiversity today has the unusual property that 85% of plant and animal species live on land rather than in the sea, and half of these live in tropical rainforests. An explosive boost to ...terrestrial diversity occurred from c. 100–50 million years ago, the Late Cretaceous and early Palaeogene. During this interval, the Earth‐life system on land was reset, and the biosphere expanded to a new level of productivity, enhancing the capacity and species diversity of terrestrial environments. This boost in terrestrial biodiversity coincided with innovations in flowering plant biology and evolutionary ecology, including their flowers and efficiencies in reproduction; coevolution with animals, especially pollinators and herbivores; photosynthetic capacities; adaptability; and ability to modify habitats. The rise of angiosperms triggered a macroecological revolution on land and drove modern biodiversity in a secular, prolonged shift to new, high levels, a series of processes we name here the Angiosperm Terrestrial Revolution.
Evolution may be dominated by biotic factors, as in the Red Queen model, or abiotic factors, as in the Court Jester model, or a mixture of both. The two models appear to operate predominantly over ...different geographic and temporal scales: Competition, predation, and other biotic factors shape ecosystems locally and over short time spans, but extrinsic factors such as climate and oceanographic and tectonic events shape larger-scale patterns regionally and globally, and through thousands and millions of years. Paleobiological studies suggest that species diversity is driven largely by abiotic factors such as climate, landscape, or food supply, and comparative phylogenetic approaches offer new insights into clade dynamics.
Infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is initiated by virus binding to the ACE2 cell-surface receptors
, followed by fusion of the virus and cell membranes to ...release the virus genome into the cell. Both receptor binding and membrane fusion activities are mediated by the virus spike glycoprotein
. As with other class-I membrane-fusion proteins, the spike protein is post-translationally cleaved, in this case by furin, into the S1 and S2 components that remain associated after cleavage
. Fusion activation after receptor binding is proposed to involve the exposure of a second proteolytic site (S2'), cleavage of which is required for the release of the fusion peptide
. Here we analyse the binding of ACE2 to the furin-cleaved form of the SARS-CoV-2 spike protein using cryo-electron microscopy. We classify ten different molecular species, including the unbound, closed spike trimer, the fully open ACE2-bound trimer and dissociated monomeric S1 bound to ACE2. The ten structures describe ACE2-binding events that destabilize the spike trimer, progressively opening up, and out, the individual S1 components. The opening process reduces S1 contacts and unshields the trimeric S2 core, priming the protein for fusion activation and dissociation of ACE2-bound S1 monomers. The structures also reveal refolding of an S1 subdomain after ACE2 binding that disrupts interactions with S2, which involves Asp614
and leads to the destabilization of the structure of S2 proximal to the secondary (S2') cleavage site.
National security policies increasingly threaten the rules that govern trade and investment flows. This problem is deeper and far more intractable than recent high-profile controversies, such as ...disputes over the Trump Administration's steel and aluminum tariffs, suggest. Governments worldwide have adopted national security policies that address an increasingly wide array of risks and vulnerabilities, including climate change; pandemic disease; cybercrime; terrorism; and threats to infrastructure, industry, and the media. These policies are also increasingly likely to conflict with trade and investment rules. In other words, while today's high-profile controversies center on alleged abuses of national security in economic law, it is the potential for goodfaith but novel national security claims that poses a more significant and permanent threat to the system. This Article is the first to map the new national security challenge and consider its implications for reforming the economic order. It demonstrates that the twenty-first-century expansion of national security policy undermines existing models for separating security measures from ordinary economic regulation. What is needed, it argues, is a new model for reintegrating the economic order with the national security state. To that end, this Article identifies reforms that allow for some oversight of increasingly novel national security claims while preserving flexibility for governments to redefine their security policies in response to twenty-first-century threats.
Oxygen heterocycles are the second most common type of heterocycles that appear as structural components of U.S. Food and Drug Administration (FDA) approved pharmaceuticals. Analysis of our database ...of drugs approved through 2017 reveals 311 distinct pharmaceuticals containing at least one oxygen heterocycle. Most prevalent among these are pyranoses, with furanoses, macrolactones, morpholines, and dioxolanes rounding off the top five. The main body of this Perspective is organized according to ring size, commencing with three- and four-membered rings and ending with macrocycles, polymers, and unusual oxygen-containing heterocycles. For each section, all oxygen heterocycle-containing drugs are presented along with a brief discussion about structural and drug application patterns.
The American democratic system of government is being put to its greatest test since the Great Depression of the 1920s and 1930s, as the country endeavors to cope with the fallout from the COVID-19 ...pandemic. That is, considerable pressure continues to build up at the fault lines of governance inherent in the country’s unique federal form of government which explicitly and implicitly expects national, state, and local levels to work together while they also may function as separate, autonomous entities to promote and provide for the general welfare. These fault lines exist where governance and service provision matters necessitate the collective attention and action of two or more levels of government. Both cooperation and conflict are possible interactive outcomes in these situations.
This article provides an early assessment of how national, state, and local governments have worked together since the onset of the COVID-19 pandemic and subsequently a “report card” of sorts on the functioning of intergovernmental relations in the U.S. at the present time. More specifically, the article will examine the current condition of interstate, interlocal, state-local, and national-state relations. While the findings and observations reported here are certainly enlightening, they should be viewed as preliminary. Followed up research should be conducted to determine if there have been any policy learning has occurred and if such information has been used in improve the quality of governance in keeping with citizen expectations of American federalism.
SARS-CoV-2 is thought to have emerged from bats, possibly via a secondary host. Here, we investigate the relationship of spike (S) glycoprotein from SARS-CoV-2 with the S protein of a closely related ...bat virus, RaTG13. We determined cryo-EM structures for RaTG13 S and for both furin-cleaved and uncleaved SARS-CoV-2 S; we compared these with recently reported structures for uncleaved SARS-CoV-2 S. We also biochemically characterized their relative stabilities and affinities for the SARS-CoV-2 receptor ACE2. Although the overall structures of human and bat virus S proteins are similar, there are key differences in their properties, including a more stable precleavage form of human S and about 1,000-fold tighter binding of SARS-CoV-2 to human receptor. These observations suggest that cleavage at the furin-cleavage site decreases the overall stability of SARS-CoV-2 S and facilitates the adoption of the open conformation that is required for S to bind to the ACE2 receptor.
Macroevolution, encompassing the deep-time patterns of the origins of modern biodiversity, has been discussed in many contexts. Non-Darwinian models such as macromutations have been proposed as a ...means of bridging seemingly large gaps in knowledge, or as a means to explain the origin of exquisitely adapted body plans. However, such gaps can be spanned by new fossil finds, and complex, integrated organisms can be shown to have evolved piecemeal. For example, the fossil record between dinosaurs and Archaeopteryx has now filled up with astonishing fossil intermediates that show how the unique plexus of avian adaptations emerged step by step over 60 Myr. New numerical approaches to morphometrics and phylogenetic comparative methods allow palaeontologists and biologists to work together on deep-time questions of evolution, to explore how diversity, morphology and function have changed through time. Patterns are more complex than sometimes expected, with frequent decoupling of species diversity and morphological diversity, pointing to the need for some new generalizations about the processes that lie behind such patterns.
The origins of modern biodiversity on land Benton, Michael J.
Philosophical transactions of the Royal Society of London. Series B. Biological sciences,
11/2010, Letnik:
365, Številka:
1558
Journal Article
Recenzirano
Odprti dostop
Comparative studies of large phylogenies of living and extinct groups have shown that most biodiversity arises from a small number of highly species-rich clades. To understand biodiversity, it is ...important to examine the history of these clades on geological time scales. This is part of a distinct ‘phylogenetic expansion’ view of macroevolution, and contrasts with the alternative, non-phylogenetic ‘equilibrium’ approach to the history of biodiversity. The latter viewpoint focuses on density-dependent models in which all life is described by a single global-scale model, and a case is made here that this approach may be less successful at representing the shape of the evolution of life than the phylogenetic expansion approach. The terrestrial fossil record is patchy, but is adequate for coarse-scale studies of groups such as vertebrates that possess fossilizable hard parts. New methods in phylogenetic analysis, morphometrics and the study of exceptional biotas allow new approaches. Models for diversity regulation through time range from the entirely biotic to the entirely physical, with many intermediates. Tetrapod diversity has risen as a result of the expansion of ecospace, rather than niche subdivision or regional-scale endemicity resulting from continental break-up. Tetrapod communities on land have been remarkably stable and have changed only when there was a revolution in floras (such as the demise of the Carboniferous coal forests, or the Cretaceous radiation of angiosperms) or following particularly severe mass extinction events, such as that at the end of the Permian.
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