Table Of Contents Page, PNAS Volume 109, Number 44

PNAS October 30, 2012

This Week in PNAS

Letters (Online Only)

QnAs

Commentaries

Perspective

Genetic and paleoanthropological evidence is in accord that today’s human population is the result of a great demic (demographic and geographic) expansion that began approximately 45,000 to 60,000 y ago in Africa and rapidly resulted in human occupation ...

Chemical Physics Of Protein Folding Special Feature (free online)

Introduction

Research Articles

Much experimental work has been devoted in comparing the folding behavior of proteins sharing the same fold but different sequence. The recent design of proteins displaying very high sequence identities but different 3D structure allows the unique ...
Studies of protein folding and the intermediates that are formed along the folding pathway provide valuable insights into the process by which an unfolded ensemble forms a functional native conformation. However, because intermediates on folding pathways ...
Recent experiments have conclusively shown that proteins are able to fold from an unknotted, denatured polypeptide to the knotted, native state without the aid of chaperones. These experiments are consistent with a growing body of theoretical work showing ...
While fast folding of small proteins has been relatively well characterized by experiments and theories, much less is known for slow folding of larger proteins, for which recent experiments suggested quite complex and rich folding behaviors. Here, we ...
The elongated three-helix bundle domains spectrin R16 and R17 fold some two to three orders of magnitude more slowly than their homologue R15. We have shown that this slow folding is due, at least in part, to roughness in the free-energy landscape of R16 ...
Internal friction, which reflects the “roughness” of the energy landscape, plays an important role for proteins by modulating the dynamics of their folding and other conformational changes. However, the experimental quantification of internal friction and ...
Markov state models constructed from molecular dynamics simulations have recently shown success at modeling protein folding kinetics. Here we introduce two methods, flux PCCA+ (FPCCA+) and sliding constraint rate estimation (SCRE), that allow accurate ...
Calmodulin is the primary calcium binding protein in living cells. Its function and structure depend strongly on calcium concentration. We used single molecule force spectroscopy by optical tweezers to study the folding of calmodulin in the ...
Many biological processes generate force, and proteins have evolved to resist and respond to tension along different force axes. Single-molecule force spectroscopy allows for molecular insight into the behavior of proteins under force and the mechanism of ...
Protein structure and function depend on a close interplay between intrinsic folding energy landscapes and the chemistry of the protein environment. Osmolytes are small-molecule compounds that can act as chemical chaperones by altering the environment in ...
We use molecular simulations using a coarse-grained model to map the folding landscape of Green Fluorescent Protein (GFP), which is extensively used as a marker in cell biology and biotechnology. Thermal and Guanidinium chloride (GdmCl) induced unfolding ...
We present an integrated experimental and computational study of the molecular mechanisms by which myristoylation affects protein folding and function, which has been little characterized to date. Myristoylation, the covalent linkage of a hydrophobic C14 ...
Advances in simulation techniques and computing hardware have created a substantial overlap between the timescales accessible to atomic-level simulations and those on which the fastest-folding proteins fold. Here we demonstrate, using simulations of four ...
Molecular dynamics simulations of protein folding or unfolding, unlike most in vitro experimental methods, are performed on a single molecule. The effects of neighboring molecules on the unfolding/folding pathway are largely ignored experimentally and ...
Intrinsically disordered proteins (IDP) are a broad class of proteins with relatively flat energy landscapes showing a high level of functional promiscuity, which are frequently regulated through posttranslational covalent modifications. Histone tails, ...
We measure the stability and folding rate of a mutant of the enzyme phosphoglycerate kinase (PGK) inside bone tissue cells as a function of temperature from 38 to 48 °C. To facilitate measurement in individual living cells, we developed a rapid laser ...
Although superoxide dismutase 1 (SOD1) stands out as a relatively soluble protein in vitro, it can be made to fibrillate by mechanical agitation. The mechanism of this fibrillation process is yet poorly understood, but attains considerable interest due to ...

Physical Sciences

Applied Physical Sciences

Euglenids exhibit an unconventional motility strategy amongst unicellular eukaryotes, consisting of large-amplitude highly concerted deformations of the entire body (euglenoid movement or metaboly). A plastic cell envelope called pellicle mediates these ...
In early stages of various pulmonary diseases, such as emphysema and fibrosis, the change in X-ray attenuation is not detectable with absorption-based radiography. To monitor the morphological changes that the alveoli network undergoes in the progression ...

Chemistry

Internal friction, which reflects the “roughness” of the energy landscape, plays an important role for proteins by modulating the dynamics of their folding and other conformational changes. However, the experimental quantification of internal friction and ...
We use molecular simulations using a coarse-grained model to map the folding landscape of Green Fluorescent Protein (GFP), which is extensively used as a marker in cell biology and biotechnology. Thermal and Guanidinium chloride (GdmCl) induced unfolding ...
We measure the stability and folding rate of a mutant of the enzyme phosphoglycerate kinase (PGK) inside bone tissue cells as a function of temperature from 38 to 48 °C. To facilitate measurement in individual living cells, we developed a rapid laser ...
Although superoxide dismutase 1 (SOD1) stands out as a relatively soluble protein in vitro, it can be made to fibrillate by mechanical agitation. The mechanism of this fibrillation process is yet poorly understood, but attains considerable interest due to ...
Human nociceptive voltage-gated sodium channel (Nav1.7), a target of significant interest for the development of antinociceptive agents, is blocked by low nanomolar concentrations of (−)-tetrodotoxin(TTX) but not (+)-saxitoxin (STX) and (+)-gonyautoxin-...

Computer Sciences

Early in development, infants learn to solve visual problems that are highly challenging for current computational methods. We present a model that deals with two fundamental problems in which the gap between computational difficulty and infant learning ...

Earth, Atmospheric, and Planetary Sciences

Firestone et al. sampled sedimentary sequences at many sites across North America, Europe, and Asia [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 106:16016–16021]. In sediments dated to the Younger Dryas onset or Boundary (YDB) approximately 12,900 ...

Physics

We examine the effect of vacancies on the phase behavior and structure of systems consisting of hard cubes using event-driven molecular dynamics and Monte Carlo simulations. We find a first-order phase transition between a fluid and a simple cubic crystal ...
We use confocal microscopy to directly observe 3D translational and rotational diffusion of tetrahedral clusters, which serve as tracers in colloidal supercooled fluids. We find that as the colloidal glass transition is approached, translational and ...
In thermophoresis, with the fluid at rest, suspensions move along a gradient of temperature. In an aqueous solution, a PEG polymer suspension is depleted from the hot region and builds a concentration gradient. In this gradient, DNA polymers of different ...
Cells often perform computations in order to respond to environmental cues. A simple example is the classic problem, first considered by Berg and Purcell, of determining the concentration of a chemical ligand in the surrounding media. On general ...

Social Sciences

Psychological and Cognitive Sciences

Languages of the world display many structural similarities. We test the hypothesis that some of these structural properties may arise from biases operating during language acquisition that shape languages over time. Specifically, we investigate whether ...
As leaders ascend to more powerful positions in their groups, they face ever-increasing demands. As a result, there is a common perception that leaders have higher stress levels than nonleaders. However, if leaders also experience a heightened sense of ...
Recent research has shown that specific areas of the human brain are activated by speech from the time of birth. However, it is currently unknown whether newborns' brains also encode and remember the sounds of words when processing speech. The present ...
Children with anxious temperament (AT) are particularly sensitive to new social experiences and have increased risk for developing anxiety and depression. The young rhesus monkey is optimal for studying the origin of human AT because it shares with humans ...
Detection and avoidance of impending obstacles is crucial to preventing head and body injuries in daily life. To safely avoid obstacles, locations of objects approaching the body surface are usually detected via the visual system and then used by the ...

Biological Sciences

Anthropology

Animal locomotion causes head rotations, which are detected by the semicircular canals of the inner ear. Morphologic features of the canals influence rotational sensitivity, and so it is hypothesized that locomotion and canal morphology are functionally ...

Applied Biological Sciences

Protein profiling has revealed the presence of glacontryphan-M, a peptide toxin identified only in the sea snail genus Conus, in the wings of Hebomoia glaucippe (HG). The wings and body of HG were homogenized and the proteins were extracted and analyzed ...
Microbial systems are being increasingly developed as production hosts for a wide variety of chemical compounds. Broader adoption of microbial synthesis is hampered by a limited number of high-yielding natural pathways for molecules with the desired ...

Biochemistry

The lactose permease (LacY) catalyzes coupled stoichiometric symport of a galactoside and an H+. Crystal structures reveal 12, mostly irregular, transmembrane α-helices surrounding a cavity with sugar- and H+- binding sites at the apex, which is ...
Synchronization of the circadian clock in cyanobacteria with the day/night cycle proceeds without an obvious photoreceptor, leaving open the question of its specific mechanism. The circadian oscillator can be reconstituted in vitro, where the activities ...
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Profile of Susan S. Golden

The X-ray crystal structure of the Head module, one-third of the Mediator of transcriptional regulation, has been determined as a complex with the C-terminal domain (CTD) of RNA polymerase II. The structure reveals multiple points of interaction with an ...
SNARE-dependent membrane fusion in eukaryotic cells requires that the heptad-repeat SNARE domains from R- and Q-SNAREs, anchored to apposed membranes, assemble into four-helix coiled-coil bundles. In addition to their SNARE and transmembrane domains, most ...
Aberrant activation of signaling by the Wnt pathway is strongly implicated in the onset and progression of numerous types of cancer. Owing to the persistent dependence of these tumors on Wnt signaling for growth and survival, inhibition of this pathway is ...
Gene expression is primarily regulated by cis-regulatory DNA elements and trans-interacting proteins. Transcription factors bind in a DNA sequence–specific manner and recruit activities that modulate the association and activity of transcription complexes ...
Recognition of methylated histone tail lysine residues by tudor domains plays important roles in epigenetic control of gene expression and DNA damage response. Previous studies revealed the binding of methyllysine in a cage of aromatic residues, but the ...
Protein arginine methyltransferases (PRMTs) play important roles in several cellular processes, including signaling, gene regulation, and transport of proteins and nucleic acids, to impact growth, differentiation, proliferation, and development. PRMT5 ...
Mammalian aminopeptidase N (APN) plays multifunctional roles in many physiological processes, including peptide metabolism, cell motility and adhesion, and coronavirus entry. Here we determined crystal structures of porcine APN at 1.85 Å resolution and ...

Biophysics and Computational Biology

Much experimental work has been devoted in comparing the folding behavior of proteins sharing the same fold but different sequence. The recent design of proteins displaying very high sequence identities but different 3D structure allows the unique ...
Studies of protein folding and the intermediates that are formed along the folding pathway provide valuable insights into the process by which an unfolded ensemble forms a functional native conformation. However, because intermediates on folding pathways ...
Recent experiments have conclusively shown that proteins are able to fold from an unknotted, denatured polypeptide to the knotted, native state without the aid of chaperones. These experiments are consistent with a growing body of theoretical work showing ...
While fast folding of small proteins has been relatively well characterized by experiments and theories, much less is known for slow folding of larger proteins, for which recent experiments suggested quite complex and rich folding behaviors. Here, we ...
The elongated three-helix bundle domains spectrin R16 and R17 fold some two to three orders of magnitude more slowly than their homologue R15. We have shown that this slow folding is due, at least in part, to roughness in the free-energy landscape of R16 ...
Internal friction, which reflects the “roughness” of the energy landscape, plays an important role for proteins by modulating the dynamics of their folding and other conformational changes. However, the experimental quantification of internal friction and ...
Markov state models constructed from molecular dynamics simulations have recently shown success at modeling protein folding kinetics. Here we introduce two methods, flux PCCA+ (FPCCA+) and sliding constraint rate estimation (SCRE), that allow accurate ...
Calmodulin is the primary calcium binding protein in living cells. Its function and structure depend strongly on calcium concentration. We used single molecule force spectroscopy by optical tweezers to study the folding of calmodulin in the ...
Many biological processes generate force, and proteins have evolved to resist and respond to tension along different force axes. Single-molecule force spectroscopy allows for molecular insight into the behavior of proteins under force and the mechanism of ...
Protein structure and function depend on a close interplay between intrinsic folding energy landscapes and the chemistry of the protein environment. Osmolytes are small-molecule compounds that can act as chemical chaperones by altering the environment in ...
We use molecular simulations using a coarse-grained model to map the folding landscape of Green Fluorescent Protein (GFP), which is extensively used as a marker in cell biology and biotechnology. Thermal and Guanidinium chloride (GdmCl) induced unfolding ...
We present an integrated experimental and computational study of the molecular mechanisms by which myristoylation affects protein folding and function, which has been little characterized to date. Myristoylation, the covalent linkage of a hydrophobic C14 ...
Advances in simulation techniques and computing hardware have created a substantial overlap between the timescales accessible to atomic-level simulations and those on which the fastest-folding proteins fold. Here we demonstrate, using simulations of four ...
Molecular dynamics simulations of protein folding or unfolding, unlike most in vitro experimental methods, are performed on a single molecule. The effects of neighboring molecules on the unfolding/folding pathway are largely ignored experimentally and ...
Intrinsically disordered proteins (IDP) are a broad class of proteins with relatively flat energy landscapes showing a high level of functional promiscuity, which are frequently regulated through posttranslational covalent modifications. Histone tails, ...
We measure the stability and folding rate of a mutant of the enzyme phosphoglycerate kinase (PGK) inside bone tissue cells as a function of temperature from 38 to 48 °C. To facilitate measurement in individual living cells, we developed a rapid laser ...
Although superoxide dismutase 1 (SOD1) stands out as a relatively soluble protein in vitro, it can be made to fibrillate by mechanical agitation. The mechanism of this fibrillation process is yet poorly understood, but attains considerable interest due to ...
Euglenids exhibit an unconventional motility strategy amongst unicellular eukaryotes, consisting of large-amplitude highly concerted deformations of the entire body (euglenoid movement or metaboly). A plastic cell envelope called pellicle mediates these ...
In thermophoresis, with the fluid at rest, suspensions move along a gradient of temperature. In an aqueous solution, a PEG polymer suspension is depleted from the hot region and builds a concentration gradient. In this gradient, DNA polymers of different ...
Cells often perform computations in order to respond to environmental cues. A simple example is the classic problem, first considered by Berg and Purcell, of determining the concentration of a chemical ligand in the surrounding media. On general ...

Cell Biology

Controlled maturation of ovarian follicles is necessary for fertility. Follicles are restrained at an immature stage until stimulated by FSH secreted by pituitary gonadotropes. FSH acts on granulosa cells within the immature follicle to inhibit apoptosis, ...
The stoichiometry and composition of membrane protein receptors are critical to their function. However, the inability to assess receptor subunit stoichiometry in situ has hampered efforts to relate receptor structures to functional states. Here, we ...
Myofibril stability is required for normal muscle function and maintenance. Mutations that disrupt myofibril stability result in individuals who develop progressive muscle wasting, or muscular dystrophy, and premature mortality. Here we present our ...

Environmental Sciences

Despite the high abundance of Archaea in the global ocean, their metabolism and biogeochemical roles remain largely unresolved. We investigated the population dynamics and metabolic activity of Thaumarchaeota in polar environments, where these ...
The world’s coral reefs are being degraded, and the need to reduce local pressures to offset the effects of increasing global pressures is now widely recognized. This study investigates the spatial and temporal dynamics of coral cover, identifies the main ...
Symbiotic relationships are widespread in nature and are fundamental for ecosystem functioning and the evolution of biodiversity. In marine environments, photosymbiosis with microalgae is best known for sustaining benthic coral reef ecosystems. Despite ...

Evolution

Variation in relative brain size is commonly interpreted as the result of selection on neuronal capacity. However, this approach ignores that relative brain size is also linked to another highly adaptive variable: body size. Considering that one-way ...
The rise of insect societies, marked by the formation of reproductive and sterile castes, represents a major unsolved mystery in evolution. Across several independent origins of sociality, the genomes of social hymenopterans share two peculiar attributes: ...

Genetics

Genetic variation between individuals has been extensively investigated, but differences between tissues within individuals are far less understood. It is commonly assumed that all healthy cells that arise from the same zygote possess the same genomic ...
The primary structure and phosphorylation pattern of the tandem Y1S2P3T4S5P6S7 repeats of the RNA polymerase II carboxyl-terminal domain (CTD) convey information about the transcription apparatus—a CTD code—to a large ensemble of CTD-binding receptor ...

Immunology

Filovirus infections can cause a severe and often fatal disease in humans and nonhuman primates, including great apes. Here, three anti-Ebola virus mouse/human chimeric mAbs (c13C6, h-13F6, and c6D8) were produced in Chinese hamster ovary and in whole ...
Naïve T cells continually recirculate between blood and secondary lymphoid organs, scanning dendritic cells (DC) for foreign antigen. Despite its importance for understanding how adaptive immune responses are efficiently initiated from rare precursors, a ...

Medical Sciences

Neural stem cells (NSCs) are considered to be the cell of origin of glioblastoma multiforme (GBM). However, the genetic alterations that transform NSCs into glioma-initiating cells remain elusive. Using a unique transposon mutagenesis strategy that ...
TGFβ activation and signaling have been extensively studied in experimental models of allergen-induced asthma as potential therapeutic targets during chronic or acute phases of the disease. Outcomes of experimental manipulation of TGFβ activity have been ...
Asymmetric cell division (ACD) is believed to be a physiological event that occurs during development and tissue homeostasis in a large variety of organisms. ACD produces two unequal daughter cells, one of which resembles a multipotent stem and/or ...
Gaucher disease (GD) is an autosomal recessive disorder caused by mutations in the acid β-glucocerebrosidase gene. To model GD, we generated human induced pluripotent stem cells (hiPSC), by reprogramming skin fibroblasts from patients with type 1 (N370S/...
More than two-thirds of breast cancers express the estrogen receptor (ER) and depend on estrogen for growth and survival. Therapies targeting ER function, including aromatase inhibitors that block the production of estrogens and ER antagonists that alter ...
Human malignant pleural mesothelioma (MPM) is considered a rare tumor, but recent estimations indicate that one-quarter million people will die of this neoplasm in Europe in the next three decades. The mineral asbestos is considered the main causative ...
Ikaros is a zinc finger-containing DNA-binding protein that plays a pivotal role in immune homeostasis through transcriptional regulation of the earliest stages of lymphocyte ontogeny and differentiation. Functional deficiency of Ikaros has been ...

Microbiology

Innate sensing of microbial components is well documented to occur at many cellular sites, including at the cell surface, in the cytosol, and in intracellular vesicles, but there is limited evidence of nuclear innate signaling. In this study we have ...
Paramyxoviruses contain glycoprotein fusion machineries that mediate membrane merger for infection. The molecular framework and mechanistic principles governing receptor-induced triggering of the machinery remain unknown. Using measles virus (MeV) fusion ...
A distinct class of infectious agents, the virophages that infect giant viruses of the Mimiviridae family, has been recently described. Here we report the simultaneous discovery of a giant virus of Acanthamoeba polyphaga (Lentille virus) that contains an ...
Cytosolic bacterial pathogens require extensive metabolic adaptations within the host to replicate intracellularly and cause disease. In phagocytic cells such as macrophages, these pathogens must respond rapidly to nutrient limitation within the harsh ...
Synthetic biology applies engineering principles to facilitate the predictable design of biological systems. Biological systems composed of modular parts with clearly defined interactions are generally easier to manipulate than complex systems exhibiting ...
In the presence of extensive DNA damage, eukaryotes activate endonucleases to fragment their chromosomes and induce apoptotic cell death. Apoptotic-like responses have recently been described in bacteria, but primarily in specialized mutant backgrounds, ...

Neuroscience

Human nociceptive voltage-gated sodium channel (Nav1.7), a target of significant interest for the development of antinociceptive agents, is blocked by low nanomolar concentrations of (−)-tetrodotoxin(TTX) but not (+)-saxitoxin (STX) and (+)-gonyautoxin-...
Children with anxious temperament (AT) are particularly sensitive to new social experiences and have increased risk for developing anxiety and depression. The young rhesus monkey is optimal for studying the origin of human AT because it shares with humans ...
Detection and avoidance of impending obstacles is crucial to preventing head and body injuries in daily life. To safely avoid obstacles, locations of objects approaching the body surface are usually detected via the visual system and then used by the ...
Mutations in the contactin-associated protein 2 (CNTNAP2) gene encoding CASPR2, a neurexin-related cell-adhesion molecule, predispose to autism, but the function of CASPR2 in neural circuit assembly remains largely unknown. In a knockdown survey of autism ...
A major physiologic sign in Parkinson disease is the occurrence of abnormal oscillations in cortico-basal ganglia circuits, which can be normalized by l-DOPA therapy. Under normal circumstances, oscillatory activity in these circuits is modulated as ...
Rat insulin promoter (RIP)-expressing neurons in the hypothalamus control body weight and energy homeostasis. However, genetic approaches to study the role of these neurons have been limited by the fact that RIP expression is predominantly found in ...
To distinguish between different models of vesicular release in brain synapses, it is necessary to know the number of vesicles of transmitter that can be released immediately at individual synapses by a high-calcium stimulus, the readily releasable pool (...
The neuropeptide oxytocin (OXT) can enhance the impact of positive social cues but may reduce that of negative ones by inhibiting amygdala activation, although it is unclear whether the latter causes blunted emotional and mnemonic responses. In two ...
Under most physiological circumstances, monocytes are excluded from parenchymal CNS tissues. When widespread monocyte entry occurs, their numbers decrease shortly after engraftment in the presence of microglia. However, some disease processes lead to ...
Chronic intermittent access to alcohol leads to the escalation of alcohol intake, similar to binge drinking in humans. Converging lines of evidence suggest that impairment of medial prefrontal cortex (mPFC) cognitive function and overactivation of the ...
It is widely appreciated that memory processing engages a wide range of molecular signaling cascades in neurons, but how these cascades are temporally and spatially integrated is not well understood. To explore this important question, we used Aplysia ...
Sensory systems across the brain are specialized for their input, yet some principles of neural organization are conserved across modalities. The pattern of anatomical connections from the primate auditory cortex to the temporal, parietal, and prefrontal ...

Pharmacology

GABAA receptors are pentameric ligand-gated ion channels involved in fast inhibitory neurotransmission and are allosterically modulated by the anxiolytic, anticonvulsant, and sedative-hypnotic benzodiazepines. Here we show that the prokaryotic homolog ...
Endothelial cell (EC) Ca2+-activated K channels (SKCa and IKCa channels) generate hyperpolarization that passes to the adjacent smooth muscle cells causing vasodilation. IKCa channels focused within EC projections toward the smooth muscle cells are ...

Physiology

Sodium-coupled substrate transport plays a central role in many biological processes. However, despite knowledge of the structures of several sodium-coupled transporters, the location of the sodium-binding site(s) often remains unclear. Several of these ...
Mechanosensitive (MS) channels are universal cellular membrane pores. Bacterial MS channels, as typified by MS channel of small conductance (MscS) from Escherichia coli (EcMscS), release osmolytes under hypoosmotic conditions. MS channels are known to be ...
Nitric oxide (NO) derived from the activity of neuronal nitric oxide synthase (NOS1) is involved in S-nitrosylation of key sarcoplasmic reticulum (SR) Ca2+ handling proteins. Deficient S-nitrosylation of the cardiac ryanodine receptor (RyR2) has a ...
Calcifying echinoid larvae respond to changes in seawater carbonate chemistry with reduced growth and developmental delay. To date, no information exists on how ocean acidification acts on pH homeostasis in echinoderm larvae. Understanding acid–base ...

Plant Biology

MicroRNAs (miRNAs) are important for plant development and stress responses. However, factors regulating miRNA metabolism are not completely understood. SICKLE (SIC), a proline-rich protein critical for development and abiotic stress tolerance of ...
The stable carbon isotope 13C is used as a universal tracer in plant eco-physiology and studies of carbon exchange between vegetation and atmosphere. Photosynthesis fractionates against 13CO2 so that source sugars (photosynthates) are on average 13C ...

Population Biology

Life expectancy is increasing in most countries and has exceeded 80 in several, as low-mortality nations continue to make progress in averting deaths. The health and economic implications of mortality reduction have been given substantial attention, but ...

Psychological and Cognitive Sciences

White matter tissue properties are highly correlated with reading proficiency; we would like to have a model that relates the dynamics of an individual’s white matter development to their acquisition of skilled reading. The development of cerebral white ...
Languages of the world display many structural similarities. We test the hypothesis that some of these structural properties may arise from biases operating during language acquisition that shape languages over time. Specifically, we investigate whether ...
Early in development, infants learn to solve visual problems that are highly challenging for current computational methods. We present a model that deals with two fundamental problems in which the gap between computational difficulty and infant learning ...

Sustainability Science

Over 50% of the total bigeye tuna (BET) landed in the Western Central Pacific Ocean is caught incidentally in the purse seine fishery and sold for canning at prices less than US$2/kg. The remainder is landed in longline fisheries directed at BET and sold ...
It has been suggested that conversion to organic farming contributes to soil carbon sequestration, but until now a comprehensive quantitative assessment has been lacking. Therefore, datasets from 74 studies from pairwise comparisons of organic vs. ...

Correction

View the cover image for PNAS Vol.109; No.44
View the cover image for PNAS Vol.109; No.44

Cover image: Pictured is the energy landscape of a folding protein, which resembles a funnel. Guided by the energetic consistency of its internal interactions, a folding protein diffuses from the top of the funnel and can follow many different folding routes before it emerges at the bottom in its most energetically stable native structure. The articles included in the Chemical Physics of Protein Folding Special Feature explore the general principles of protein folding from the diverse perspectives of molecular biology, organic chemistry, computer science, and theoretical physics. See the Introduction to this special feature by Peter G. Wolynes, William A. Eaton, and Alan R. Fersht on pages 17770–17771. Image courtesy of Fiona Kim (Virginia Polytechnic Institute and State University, Blacksburg, VA), Bobby Kim, and Nick Schafer (Rice University, Houston, TX).

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