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961.
Karen L. Baab Sarah E. Freidline Steven L. Wang Timothy Hanson 《American journal of physical anthropology》2010,141(1):97-115
Variation in cranial robusticity among modern human populations is widely acknowledged but not well‐understood. While the use of “robust” cranial traits in hominin systematics and phylogeny suggests that these characters are strongly heritable, this hypothesis has not been tested. Alternatively, cranial robusticity may be a response to differences in diet/mastication or it may be an adaptation to cold, harsh environments. This study quantifies the distribution of cranial robusticity in 14 geographically widespread human populations, and correlates this variation with climatic variables, neutral genetic distances, cranial size, and cranial shape. With the exception of the occipital torus region, all traits were positively correlated with each other, suggesting that they should not be treated as individual characters. While males are more robust than females within each of the populations, among the independent variables (cranial shape, size, climate, and neutral genetic distances), only shape is significantly correlated with inter‐population differences in robusticity. Two‐block partial least‐squares analysis was used to explore the relationship between cranial shape (captured by three‐dimensional landmark data) and robusticity across individuals. Weak support was found for the hypothesis that robusticity was related to mastication as the shape associated with greater robusticity was similar to that described for groups that ate harder‐to‐process diets. Specifically, crania with more prognathic faces, expanded glabellar and occipital regions, and (slightly) longer skulls were more robust than those with rounder vaults and more orthognathic faces. However, groups with more mechanically demanding diets (hunter‐gatherers) were not always more robust than groups practicing some form of agriculture. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc. 相似文献
962.
In eukaryotic cells, neutral lipids serve as major energy storage molecules; however, in Plasmodium falciparum, a parasite responsible for causing malaria in humans, neutral lipids may have other functions during the intraerythrocytic stage of the parasite life cycle. Specifically, experimental data suggest that neutral lipid structures behave as a catalyst for the crystallization of hemozoin, a detoxification byproduct of several blood-feeding organisms, including malaria parasites. Synthetic neutral lipid droplets (SNLDs) were produced by depositing a lipid blend solution comprised of mono- and diglycerides onto an aqueous surface. These lipid droplets are able to mediate the production of brown pigments that are morphologically and chemically identical to hemozoin. The partitioning of heme into these SNLDs was examined by employing Nile Red, a lipid specific dye. Soluble ferriprotoporphyrin IX was observed to spontaneously localize to the lipid droplets, partitioning in a pH-dependent manner with an estimated log P of 2.6. Interestingly, the pH profile of heme partitioning closely resembles that of β-hematin formation. Differential scanning calorimetry and kinetic studies demonstrated that the SNLDs provide a unique environment that promotes hemozoin formation. SNLD-mediated formation of the malaria pigment displayed an activation energy barrier lower than those of individual lipid components. In particular, lipid droplets composed of diglycerides displayed activation barriers lower than those composed of monoglycerides. This difference was attributed to the greater fluidity of these lipids. In conjunction with the known pattern of lipid body proliferation, it is suggested that neutral lipid structures within the digestive vacuole not only are the location of in vivo hemozoin formation but are also essential for the survival of the parasite by functioning as a kinetically competent and site specific mediator for heme detoxification. 相似文献
963.
964.
Timothy D. Fenn Michael J. Schnieders Axel T. Brunger Vijay S. Pande 《Biophysical journal》2010,98(12):2984-2992
We recently developed a polarizable atomic multipole refinement method assisted by the AMOEBA force field for macromolecular crystallography. Compared to standard refinement procedures, the method uses a more rigorous treatment of x-ray scattering and electrostatics that can significantly improve the resultant information contained in an atomic model. We applied this method to high-resolution lysozyme and trypsin data sets, and validated its utility for precisely describing biomolecular electron density, as indicated by a 0.4-0.6% decrease in the R- and Rfree-values, and a corresponding decrease in the relative energy of 0.4-0.8 Kcal/mol/residue. The re-refinements illustrate the ability of force-field electrostatics to orient water networks and catalytically relevant hydrogens, which can be used to make predictions regarding active site function, activity, and protein-ligand interaction energies. Re-refinement of a DNA crystal structure generates the zigzag spine pattern of hydrogen bonding in the minor groove without manual intervention. The polarizable atomic multipole electrostatics model implemented in the AMOEBA force field is applicable and informative for crystal structures solved at any resolution. 相似文献
965.
Ibanez-Garcia D Requejo-Isidro J Webb MR West TG French P Ferenczi MA 《Biophysical journal》2010,99(7):2163-2169
Fluorescence lifetime imaging microscopy is used to demonstrate that different loads applied to a muscle fiber change the microenvironment of the nucleotide binding pocket of myosin. Permeabilized skeletal muscle fibers in rigor were labeled with a fluorescent ATP analog, 3′-DEAC-propylenediamine (pda)-ATP (3′-O-{N-[3-(7-diethylaminocoumarin-3-carboxamido)propyl]carbamoyl}ATP), which was hydrolyzed to the diphosphate. Cycles of small-amplitude stretches and releases (<1% of muscle segment length) were synchronized with fluorescence lifetime imaging and force measurements to correlate the effect of force on the lifetime of the ATP analog bound to the actomyosin complex. Analysis of the fluorescence decay resolved two lifetimes, corresponding to the free nucleotide DEAC-pda-ATP (τ1 = 0.47 ± 0.03 ns; mean ± SD) and nucleotide bound to the actomyosin complex (τ2 = 2.21 ± 0.06 ns at low strain). Whereas τ1 did not change with force, τ2 showed a linear dependence with the force applied to the muscle of 0.43 ± 0.05 ps/kPa. Hence, the molecular environment of the nucleotide binding pocket of myosin is directly affected by a change of length applied at the ends of the fiber segments. These changes may help explain how force modulates the actomyosin ATPase cycle and thus the physiology and energetics of contraction. 相似文献
966.
Feng He Timothy E. Saunders Ying Wen David Cheung Pieter Rein ten Wolde Jun Ma 《Biophysical journal》2010,99(3):697-707
Morphogen gradients, which provide positional information to cells in a developing tissue, could in principle adopt any nonuniform profile. To our knowledge, how the profile of a morphogen gradient affects positional precision has not been well studied experimentally. Here, we compare the positional precision provided by the Drosophila morphogenetic protein Bicoid (Bcd) in wild-type (wt) embryos with embryos lacking an interacting cofactor. The Bcd gradient in the latter case exhibits decreased positional precision around mid-embryo compared with its wt counterpart. The domain boundary of Hunchback (Hb), a target activated by Bcd, becomes more variable in mutant embryos. By considering embryo-to-embryo, internal, and measurement fluctuations, we dissect mathematically the relevant sources of fluctuations that contribute to the error in positional information. Using this approach, we show that the defect in Hb boundary positioning in mutant embryos is directly reflective of an altered Bcd gradient profile with increasing flatness toward mid-embryo. Furthermore, we find that noise in the Bcd input signal is dominated by internal fluctuations but, due to time and spatial averaging, the spatial precision of the Hb boundary is primarily affected by embryo-to-embryo variations. Our results demonstrate that the positional information provided by the wt Bcd gradient profile is highly precise and necessary for patterning precision. 相似文献
967.
968.
Spotted knapweed (Centaurea stoebe) is found in over 3 million ha of rangeland and forests across North America, and evidence supporting the use of biological
control as a regional method to reduce infestations and their associated impacts remains inconclusive. Several species of
insects have been reported to reduce plant densities in some areas; however, rigorous studies that test combinations of these
species and the influence of resource availability are lacking. We examined the singular and combined effects of herbivory
by a root weevil (Cyphocleonus achates) and a flower head weevil (Larinus minutus) on the growth and flower production of C. stoebe. We also manipulated soil resource fertility as an additional factor that could explain the outcomes of contradictory biological
control herbivore effects on C. stoebe. In a greenhouse study, herbivory by C. achates decreased flower production for plants across all resource environments. In a caged common garden study, the negative effects
of herbivory also did not interact with soil nutrient status. However, the presence of plant competition further decreased
knapweed growth, and the negative effects of concurrent herbivory by C. achates and L. minutus on plant biomass and flower production were additive. Derived within the context of variable levels of soil nutrient availability
and competing vegetation, these results support the cumulative stress hypothesis and the contention that combined above- and
belowground herbivory can reduce spotted knapweed densities and reduce the ecological and economic impacts of this species
in rangelands of western North America. 相似文献
969.
Jake V. Bailey Timothy D. Raub A. Nele Meckler Benjamin K. Harrison Theresa M.D. Raub Abigail M. Green Victoria J. Orphan 《Palaeogeography, Palaeoclimatology, Palaeoecology》2010,285(1-2):131-142
Pleistocene-age methane seep carbonates from the Eel River Basin, California contain aggregate-like structures composed of tightly-packed hollow spheres that morphologically resemble syntrophic archaeal–bacterial consortia known to catalyze the anaerobic oxidation of methane (AOM). Tetragonal microstructures also present in the carbonates resemble seep-endemic Methanosarcinales cell clusters. Despite morphological similarities to the seep-endemic microbes that likely mediated the authigenesis of Eel River Basin carbonates and sulfides, detailed petrographic, SEM, and magnetic microscopic imaging, remanence rock magnetism, laser Raman, and energy dispersive X-ray spectroscopy, suggest that these microstructures are not microfossils, but rather mineral structures that result from the diagenetic alteration of euhedral Fe-sulfide framboids. Electron microscopy shows that during diagenesis, reaction rims composed of Fe oxide form around framboid microcrystalites. Subsequent dissolution of greigite or pyrite crystals leaves behind hollow cell-like casings (external molds) — a transformation that occurs on timescales of ~100 kyr or less. Despite their superficial resemblance to morphologically-distinctive extant microbes in local sediments, the presence of acellular precursor grains, as well as of partially-altered transitional forms, complicate the interpretation of these and other framboidal microstructures that have been reported from the rock record. 相似文献
970.