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"Owen, R."
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Structural analysis of a nanoparticle containing a lipid bilayer used for detergent-free extraction of membrane proteins
In the past few years there has been a growth in the use of nanoparticles for stabilizing lipid membranes that contain embedded proteins. These bionanoparticles provide a solution to the challenging problem of membrane protein isolation by maintaining a lipid bilayer essential to protein integrity and activity. We have previously described the use of an amphipathic polymer （poly（styrene-co-maleic add）, SMA） to produce discoidal nanoparticles with a lipid bilayer core containing the embedded protein. However the structure of the nanoparticle itself has not yet been determined. This leaves a major gap in understanding how the SMA stabilizes the encapsulated bilayer and how the bilayer relates physically and structurally to an unencapsulated lipid bilayer. In this paper we address this issue by describing the structure of the SMA lipid particle （SMALP） using data from small angle neutron scattering （SANS）, electron microscopy （EM）, attenuated total reflection Fourier transform infrared spectroscopy （ATR-FTIR）, differential scanning calorimetry （DSC） and nuclear magnetic resonance spectroscopy （NMR）. We show that the particle is disc shaped containing a polymer ＂bracelet＂ encircling the lipid bilayer. The structure and orientation of the individual components within the bilayer and polymer are determined showing that styrene moieties within SMA intercalate between the lipid acyl chains. The dimensions of the encapsulated bilayer are also determined and match those measured for a natural membrane. Taken together, the description of the structure of the SMALP forms the foundation for future development and applications of SMALPs in membrane protein production and analysis.
Journal Article
The Underside of Order: Race in the Constitution of International Order
While there is increasing recognition of the role of race in shaping global politics, the extent to which the construction and operation of international order is entangled with race remains underexplored. In this article, I argue for the centrality of race and racialization in understanding the constitution of international order by theorizing the constitutive connections between race and international order and showing how the two can be examined as intertwined. I do this, first, by articulating conceptualizations of both international order and race that center on processes of regulation and regularization. Second, I bring these together to suggest that race be understood as a form of order that functions to reproduce a historically emergent form of hierarchy and domination across a range of spaces and contexts. Third, I operationalize these conceptualizations by outlining and historicizing some of the key features of this racialized and racializing international order, specifically coloniality, the racial state, and racial capitalism, and thereby illustrate important aspects of the persistence of this order. Centering race in the study of international order, I suggest, helps us better understand how racializing hierarchies and racialized inequalities persist in the present and are reproduced through structures and practices of international order.
Journal Article
Introduction to modeling in wildlife and resource conservation
CD-ROM contains : Models -- True BASIC programming language [trial version]
Environmental dynamics during the onset of the Middle Stone Age in eastern Africa
The Olorgesailie basin in the southern Kenya rift valley contains sediments dating back to 1.2 million years ago, preserving a long archaeological record of human activity and environmental conditions. Three papers present the oldest East African evidence of the Middle Stone Age (MSA) and elucidate the system of technology and behavior associated with the origin of
Homo sapiens
. Potts
et al.
present evidence for the demise of Acheulean technology that preceded the MSA and describe variations in late Acheulean hominin behavior that anticipate MSA characteristics. The transition to the MSA was accompanied by turnover of large mammals and large-scale landscape change. Brooks
et al.
establish that ∼320,000 to 305,000 years ago, the populations in eastern Africa underwent a technological shift upon procurement of distantly sourced obsidian for toolmaking, indicating the early development of social exchange. Deino
et al.
provide the chronological underpinning for these discoveries.
Science
, this issue p.
86
, p.
90
, p.
95
Changes in fauna, landscapes, and climate were associated with novel adaptive behaviors in the earliest
Homo sapiens
.
Development of the African Middle Stone Age (MSA) before 300,000 years ago raises the question of how environmental change influenced the evolution of behaviors characteristic of early
Homo sapiens
. We used temporally well-constrained sedimentological and paleoenvironmental data to investigate environmental dynamics before and after the appearance of the early MSA in the Olorgesailie basin, Kenya. In contrast to the Acheulean archeological record in the same basin, MSA sites are associated with a markedly different faunal community, more pronounced erosion-deposition cycles, tectonic activity, and enhanced wet-dry variability. Aspects of Acheulean technology in this region imply that, as early as 615,000 years ago, greater stone material selectivity and wider resource procurement coincided with an increased pace of land-lake fluctuation, potentially anticipating the adaptability of MSA hominins.
Journal Article
Environmental context dependency in species interactions
Ecological interactions are not uniform across time and can vary with environmental conditions. Yet, interactions among species are often measured with short-term controlled experiments whose outcomes can depend greatly on the particular environmental conditions under which they are performed. As an alternative, we use empirical dynamic modeling to estimate species interactions across a wide range of environmental conditions directly from existing long-term monitoring data. In our case study from a southern California kelp forest, we test whether interactions between multiple kelp and sea urchin species can be reliably reconstructed from time-series data and whether those interactions vary predictably in strength and direction across observed fluctuations in temperature, disturbance, and low-frequency oceanographic regimes. We show that environmental context greatly alters the strength and direction of species interactions. In particular, the state of the North Pacific Gyre Oscillation seems to drive the competitive balance between kelp species, asserting bottom-up control on kelp ecosystem dynamics. We show the importance of specifically studying variation in interaction strength, rather than mean interaction outcomes, when trying to understand the dynamics of complex ecosystems. The significant context dependency in species interactions found in this study argues for a greater utilization of long-term data and empirical dynamic modeling in studies of the dynamics of other ecosystems.
Journal Article
mpmsim: An R package for simulating matrix population models
Matrix population models (MPMs) are widely used in ecology and evolution to explore population dynamics, including assessing management impacts and extinction risk. In comparative studies, MPMs can be used to test life‐history theory or investigate macro‐evolutionary patterns in demographic traits.
Simulated MPMs can help researchers explore the effects of life cycle structure, vital rate trajectories and uncertainty in transition rates due to sampling error. They are also valuable teaching tools.
The mpmsim R package enables users to simulate random or semi‐random Lefkovitch and Leslie MPMs based on life history archetypes or mortality and reproductive output patterns. It also allows the exploration of sampling error effects and uses parametric bootstrapping to calculate confidence intervals for matrix‐derived estimates.
mpmsim provides a convenient toolset for addressing questions about MPMs and life history, with full documentation and user‐friendly vignettes.
Journal Article