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排序方式: 共有190条查询结果,搜索用时 31 毫秒
31.
W R Guirguis 《BMJ (Clinical research ed.)》1986,293(6547):587-588
32.
Matthew N. Zipple Eila K. Roberts Susan C. Alberts Jacinta C. Beehner 《Evolutionary anthropology》2019,28(3):114-125
Sexually selected infanticide has been the subject of intense empirical and theoretical study for decades; a related phenomenon, male‐mediated prenatal loss, has received much less attention in evolutionary studies. Male‐mediated prenatal loss occurs when inseminated or pregnant females terminate reproductive effort following exposure to a nonsire male, either through implantation failure or pregnancy termination. Male‐mediated prenatal loss encompasses two sub‐phenomena: sexually selected feticide and the Bruce effect. In this review, we provide a framework that explains the relationship between feticide and the Bruce effect and describes what is known about the proximate and ultimate mechanisms involved in each. Using a simple model, we demonstrate that male‐mediated prenatal loss can provide greater reproductive benefits to males than infanticide. We therefore suggest that, compared to infanticide, male‐mediated prenatal loss may be more prevalent in mammalian species and may have played a greater role in their social evolution than has previously been documented. 相似文献
33.
34.
Transcranial direct current stimulation (TDCS) is a brain stimulation tool that is portable, painless, inexpensive, apparently safe, and with potential long-term efficacy. Recent results obtained from TDCS experiments offer exciting possibilities for the enhancement and treatment of normal or impaired abilities, respectively. We discuss new neuroethical problems that have emerged from the usage of TDCS, and also focus on one of the most likely future applications of TDCS: enhancing learning and cognition in children with typical and atypical development. 相似文献
35.
Noah Snyder-Mackler Jacinta C. Beehner Thore J. Bergman 《International journal of primatology》2012,33(5):1054-1068
Multilevel societies, identified by two or more nested levels (or modules) of organization, have been touted as some of the most complex social systems. However, few empirical studies have effectively quantified the association patterns that delineate the various levels in such societies. In particular, the multiple levels of gelada society were first described >3 decades ago, yet no operational definitions exist for the higher levels, i.e., levels above the one-male unit. In geladas, multiple units form aggregations that fission and fuse throughout the day, and throughout the year, blurring the distinctions between previously described higher social levels: teams, bands, and communities. Here we use 5?yr of data on the daily composition of a population of geladas living in the Simien Mountains National Park, Ethiopia to test the hypothesis that higher levels of gelada organization are discrete entities. If gelada aggregations are nothing more than a group of units that share a home range, then we expect a continuous distribution of unit association. If, however, gelada aggregations are indeed discrete organizational levels, then we expect discontinuity in the patterns of association. We found significant discontinuity at the 50% association level, indicating a sharp distinction between members of the same band (>50% association) and members of the same community (<50% association). We also found evidence that recently fissioned units form teams that associate significantly more than other band members. Thus, despite their extremely fluid social organization, gelada social levels are nevertheless clearly identifiable and quantifiable. Based on these results, we suggest that gelada society is an extremely flexible, multilevel society with fission–fusion dynamics, and as such gelada society presents an unusual example for understanding the evolution of modular societies. 相似文献
36.
Chang CF Chou HT Lin YJ Lee SJ Chuang JL Chuang DT Huang TH 《The Journal of biological chemistry》2006,281(38):28345-28353
The homo-24-meric dihydrolipoyl transacylase (E2) scaffold of the human branched-chain alpha-ketoacid dehydrogenase complex (BCKDC) contains the lipoyl-bearing domain (hbLBD), the subunit-binding domain (hbSBD) and the inner core domain that are linked to carry out E2 functions in substrate channeling and recognition. In this study, we employed NMR techniques to determine the structure of hbSBD and dynamics of several truncated constructs from the E2 component of the human BCKDC, including hbLBD (residues 1-84), hbSBD (residues 111-149), and a di-domain (hbDD) (residues 1-166) comprising hbLBD, hbSBD and the interdomain linker. The solution structure of hbSBD consists of two nearly parallel helices separated by a long loop, similar to the structures of the SBD isolated from other species, but it lacks the short 3(10) helix. The NMR results show that the structures of hbLBD and hbSBD in isolated forms are not altered by the presence of the interdomain linker in hbDD. The linker region is not entirely exposed to solvent, where amide resonances associated with approximately 50% of the residues are observable. However, the tethering of these two domains in hbDD significantly retards the overall rotational correlation times of hbLBD and hbSBD, changing from 5.54 ns and 5.73 ns in isolated forms to 8.37 ns and 8.85 ns in the linked hbDD, respectively. We conclude that the presence of the interdomain linker restricts the motional freedom of the hbSBD more significantly than hbLBD, and that the linker region likely exists as a soft rod rather than a flexible string in solution. 相似文献
37.
Human translin is a conserved protein, unique in its ability to bind both RNA and DNA. Interestingly, GTP binding has been implicated as a regulator of RNA/DNA binding function of mouse translin (TB-RBP). We cloned and overexpressed the translin orthologue from Drosophila melanogaster and compared its DNA/RNA binding properties in relation to GTP effects with that of human protein. Human translin exhibits a stable octameric state and binds ssDNA/RNA/dsDNA targets, all of which get attenuated when GTP is added. Conversely, Drosophila translin exhibits a stable dimeric state that assembles into a suboctameric (tetramer/hexamer) form and fails to bind ssDNA and RNA targets. Interestingly enough, CD spectral analyses, partial protease digestion profile revealed GTP-specific conformational changes in human translin, whereas the same were largely missing in Drosophila protein. Isothermal calorimetry delineated specific heat changes associated with GTP binding in human translin, which invoked subunit "loosening" in its octamers; the same effect was absent in Drosophila protein. We propose that GTP acts as a specific molecular "switch" that modulates the nucleic acid binding function selectively in human translin, perhaps by affecting its octameric configuration. 相似文献
38.
Tracy A. Tebb Shiao-Wen Tsai Veronica Glattauer Jacinta F. White John A. M. Ramshaw Jerome A. Werkmeister 《Cytotechnology》2006,52(2):99-106
A method for the preparation of bioresorbable collagen beads with an open porous structure is presented. These beads were
prepared from collagen-alginate composite beads by removal of the alginate component. These collagen beads were suitable for
rapid proliferation of chondrocytes in a dynamic, spinner culture system. Histology and immuno-histology showed that biochemical
markers of chondrocytes are present during this cell proliferation, indicating that there was control of phenotype and that
cell de-differentiation had not occurred. Unlike other 3-D scaffolds that have been used, the cells were amplified from very
low cell densities and were able to proliferate freely without loss of phenotype.
Tracy A. Tebb, Shiao-Wen Tsai, Veronica Glattauer and Jacinta F. White have made equal contributions to this study. 相似文献
39.
Chad A. Brautigam R. Max Wynn Jacinta L. Chuang David T. Chuang 《The Journal of biological chemistry》2009,284(19):13086-13098
The human pyruvate dehydrogenase complex (PDC) is a 9.5-megadalton
catalytic machine that employs three catalytic components, i.e.
pyruvate dehydrogenase (E1p), dihydrolipoyl transacetylase (E2p), and
dihydrolipoamide dehydrogenase (E3), to carry out the oxidative
decarboxylation of pyruvate. The human PDC is organized around a 60-meric
dodecahedral core comprising the C-terminal domains of E2p and a noncatalytic
component, E3-binding protein (E3BP), which specifically tethers E3 dimers to
the PDC. A central issue concerning the PDC structure is the subunit
stoichiometry of the E2p/E3BP core; recent studies have suggested that the
core is composed of 48 copies of E2p and 12 copies of E3BP. Here, using an
in vitro reconstituted PDC, we provide densitometry, isothermal
titration calorimetry, and analytical ultracentrifugation evidence that there
are 40 copies of E2p and 20 copies of E3BP in the E2p/E3BP core.
Reconstitution with saturating concentrations of E1p and E3 demonstrated 40
copies of E1p heterotetramers and 20 copies of E3 dimers associated with the
E2p/E3BP core. To corroborate the 40/20 model of this core, the
stoichiometries of E3 and E1p binding to their respective binding domains were
reexamined. In these binding studies, the stoichiometries were found to be
1:1, supporting the 40/20 model of the core. The overall maximal stoichiometry
of this in vitro assembled PDC for E2p:E3BP:E1p:E3 is 40:20:40:20.
These findings contrast a previous report that implicated that two E3-binding
domains of E3BP bind simultaneously to a single E3 dimer (Smolle, M., Prior,
A. E., Brown, A. E., Cooper, A., Byron, O., and Lindsay, J. G. (2006) J.
Biol. Chem. 281, 19772–19780).The human pyruvate dehydrogenase complex
(PDC)3 resides in
mitochondria and catalyzes the oxidative decarboxylation of pyruvate to yield
acetyl-CoA and reducing equivalents (NADH), serving as a link between
glycolysis and the Krebs cycle
(1–3).
The PDC is a large (∼9.5 MDa) catalytic machine comprising multiple
protein components. The three catalytic components are pyruvate dehydrogenase
(E1p), dihydrolipoyl transacetylase (E2p), and dihydrolipoamide dehydrogenase
(E3), with E3 being a common component between different α-keto acid
dehydrogenase complexes. The two regulatory enzymes in the PDC are the
isoforms of pyruvate dehydrogenase kinase and pyruvate dehydrogenase
phosphatase.The PDC is organized around a structural core, which includes the
C-terminal domains of E2p and a noncatalytic component that specifically binds
E3, i.e. the E3-binding protein (E3BP). To this E2p/E3BP core,
multiple copies of the other PDC components are tethered through noncovalent
interactions. Each E2p subunit contains two consecutive N-terminal lipoic
acid-bearing domains (LBDs), termed L1 and L2, followed by the E1p-binding
domain (E1pBD) and the C-terminal inner-core/catalytic domain, with these
independent domains connected by unstructured linkers. Similarly, each E3BP
subunit consists of a single N-terminal LBD (referred to as L3), the
E3-binding domain (E3BD), and the noncatalytic inner core domain. Together,
the inner core domains of E2p and E3BP assemble to form the dodecahedral
60-meric E2p/E3BP core. The role of the E1pBD and E3BD domains is to tether
E1p and E3, respectively, to the periphery of the E2p/E3BP core. It is
presumed that the LBDs (L1, L2, and L3) shuttle between the active sites of
the three catalytic components of the PDC during the oxidative decarboxylation
cycle (4). The eukaryotic PDC
is unique among α-keto acid dehydrogenase complexes in its requirement
for E3BP; prokaryotic PDCs employ the single subunit-binding domain to secure
either E1p or E3 to the complex
(5).Using a “divide-and-conquer” approach, a wealth of structural
information on the PDC has been accumulated recently. High-resolution crystal
structures are available for the human E1p
(6–8)
and E3 components (9). A model
for the human E2p has been constructed based on an 8.8-Å electron
density map available from cryo-electron microscopy
(10). Additionally, solution
and crystal structures of the L1 and L2 domains of E2p have been determined
(11–13),
and the high-resolution crystal structures of the E3BD
(14,
15), pyruvate dehydrogenase
kinase isoforms 1–4 (12,
16–18),
and pyruvate dehydrogenase phosphatase isoform 1
(19) are known. Therefore,
atomic models are available for almost all components and domains of the
mammalian PDC.With the successes of the above structural approach, attention has turned
to the overall structure of the PDC. There are two outstanding questions as
follows. What are the subunit and overall catalytic component stoichiometries?
What are the positions and orientations of the components in this large
catalytic machine? Yu et al.
(10) recently determined the
cryo-EM structure of a PDC core comprising only human E2p subunits. Like yeast
E2p, human E2p adopts a dodecahedral structure composed of 60 E2p proteins;
each face of the dodecahedron has a large gap. Although this structure is
highly informative, the composition of this core deviates substantially from
that of the native PDC, because no E3BP subunits are present in the core
structure. Based on the similar structure of the dodecahedral yeast PDC, a
hypothesis was formed that, in human PDC, 12 copies of E3BP bind in the 12
gaps, which is termed the “60/12” model
(20). Biophysical studies on
complexes of E2p and E3BP later negated the 60/12 model; Hiromasa et
al. (21) therefore
posited an alternative, the “48/12” model, in which the
dodecahedral core includes 48 E2p subunits and 12 E3BP proteins. A further
source of conjecture is how many E1p and E3 components bind to the periphery
of the PDC. If one binding domain binds to one peripheral catalytic component,
a maximally occupied 60/12 PDC would harbor 60 E1p heterotetramers and 12 E3
dimers (or 48 E1ps and 12 E3s in the 48/12 model). The notion of such 1:1
binding is supported by the preponderance of available biophysical evidence.
Specifically, two crystal structures, site-directed mutagenesis, and
calorimetric measurements describe a 1:1 interaction between E3BD and E3
(14,
15). Also, although no
structures are available for the human E1p-E1pBD complex, a crystal structure
of the homologs of these proteins from Bacillus stearothermophilus
also demonstrates a 1:1 interaction between the E1pBD of E2p and the E1p
heterotetramer (22). In
addition, ITC experiments performed on the bacterial E1p and the cognate
subunit-binding domain indicate a 1:1 association
(23). At variance with the
above observations, a different subunit stoichiometry has been proposed by
Smolle et al. (24,
25). Their evidence suggests
that two binding domains bind for every peripheral component; such an
arrangement potentially yields a PDC with half as many peripheral components
bound.This study was undertaken to ascertain the subunit and component
stoichiometries of the human PDC, particularly with regard to interactions
between the E3BD and the E3 dimer. We show that quantification of bands on an
SDS-polyacrylamide gel of a PDC reconstituted at saturating E1p and E3
concentrations supports neither the 60/12 nor the 48/12 model. Instead, a
“40/20” model is proposed, and subsequent ITC and analytical
ultracentrifugation (AUC) data corroborate this new model. In addition,
results from electrophoretic mobility shift assays, ITC, and AUC presented
here uniformly show a 1:1 interaction between E3BD and the E3 dimer as well as
between E1pBD and the E1p heterotetramer. The implications of this 1:1 binding
stoichiometry for the macromolecular assembly of the PDC are discussed. 相似文献
40.
Laura L. Dugan Sameh S. Ali Grigoriy Shekhtman Amanda J. Roberts Jacinta Lucero Kevin L. Quick M. Margarita Behrens 《PloS one》2009,4(5)