共查询到20条相似文献,搜索用时 15 毫秒
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Keith M. Meek 《Biophysical reviews》2009,1(2):83-93
Corneal collagen has a number of properties that allow it to fulfil its role as the main structural component within the tissue. Fibrils are narrow, uniform in diameter and precisely organised. These properties are vital to maintain transparency and to provide the biomechanical prerequisites necessary to sustain shape and provide strength. This review describes the structure and arrangement of corneal collagen from the nanoscopic to the macroscopic level, and how this relates to the maintenance of the form and transparency of the cornea. 相似文献
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Dworkin J 《Molecular microbiology》2010,78(4):792-795
Bacteria exhibit a wide variety of morphologies. This could simply be a consequence of an elaboration of bacterial cellular architecture akin to the famous decorative but not structurally essential Spandrels in the Basilica di San Marco in Venice that are a side-effect of an adaptation, rather than a direct product of natural selection. However, it is more likely that particular morphologies facilitate a specific function in cellular physiology. Two recent publications including one in this issue of Molecular Microbiology and another in Cell provide new insights into the molecular basis for the helical shape of the bacterium Helicobacter pylori and the role of this shape in pathogenesis. They identify a novel endopeptidase that is necessary to generate the helical shape by processing the peptidoglycan and report that catalytically inactive mutants lead to defects in colonization that appear to be independent of an effect on cellular motility. Here, we put these findings in the context of some of what is known about peptidoglycan and cell shape and suggest that the role of this endopeptidase in forming coccoid morphology may be critical for pathogenesis. 相似文献
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Copper-albumin: What is its functional role? 总被引:1,自引:0,他引:1
The small copper fraction in animal blood that is bound to albumin protein is generally considered to have a transport role for the metal. However, several studies have concluded that copper ion incorporation into copper-enzymes requires caeruloplasmin to act as the transport form. The kinetic rates of Cu(albumin) reactions are also not in keeping with a general transport function. Only in the portal bloodstream does the Cu(albumin) appear to have a well-established transport role, i.e. in delivering the metal ions from the intestine to the liver. Thereafter the evidence as to its function is less certain; it could act as a storage form of the metal or have no role at all. Similar considerations apply to other metal-albumin fractions e.g. those of zinc and nickel. 相似文献
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Wills MA Fortey RA 《BioEssays : news and reviews in molecular, cellular and developmental biology》2000,22(12):1142-1152
Considering the enormous diversity of living organisms, representing mostly untapped resources for studying ecological, ontogenetic and phylogenetic patterns and processes, why should evolutionary biologists concern themselves with the remains of animals and plants that died out tens or even hundreds of millions of years ago? The reason is that important new insights into some of the most vexing evolutionary questions are being revealed at the interfaces of palaeontology, developmental biology and molecular biology. Attempts to synthesise information from these disciplines, however, often encounter their greatest hurdles in considerations of the radiation of the Metazoa. Ongoing challenges relate to the origins of body plans, the relationships of the metazoan phyla and the timing of major evolutionary radiations. Palaeontology not only has its own unique contributions to the study of evolutionary processes, but provides a lynchpin for many of the emerging techniques. 相似文献
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V D Barbu 《Comptes rendus des séances de la Société de biologie et de ses filiales》1991,185(5):278-289
The role of mevalonate in the control of DNA synthesis during the cell cycle has been studied and has lead to the detection of isoprenylated proteins. These proteins are modified by a polyisoprenoid (farnesyl or geranylgeranyl) moiety via a thioether linkage. This modification is required for the following steps of the post-translational maturation of these proteins: proteolysis of the last three C-terminal amino-acids and carboxymethylation of the Cysteine-COOH. The isoprenylation could play a role in the membrane localisation of these proteins. Farnesylated proteins present a C-terminal CAAX domain. Moreover, the farnesylation is required for their biological activity independently of the membrane localization (Prelamine A, p21ras(Val 12)). Among geranylgeranyl proteins, two types of C-terminal sequences have been found: one with the motif CAAX, the other with the motif CC or CXC. In the last type, both Cysteines are geranylgeranylated. The hydrophobicity of the geranylgeranyl moiety leads to the membrane attachment, without any specificity. Moreover, geranylgeranylation as well as farnesylation seem important for protein-protein interactions. Among the identified isoprenylated proteins, the lamins, gamma-subunits of G proteins and the numerous (if not all) members of the Ras superfamily were characterized. The exact role of isoprenylation is still uncertain but it seems to affect the membrane localization and the protein-protein interactions. 相似文献
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According to the thermodynamic hypothesis, the native state of proteins is that in which the free energy of the system is at its lowest, so that at normal temperature and pressure, proteins evolve to that state. We selected four proteins representative of each of the four classes, and for each protein make four simulations, one starting from the native structure and the other three starting from the structure obtained by threading the sequence of one protein onto the native backbone fold of the other three proteins. Because of their large conformational distances with respect to the native structure, the three alternative initial structures cannot be considered as local minima within the native ensemble of the corresponding protein. As expected, the initial native states are preserved in the .5?μs simulations performed here and validate the simulations. On the other hand, when the initial state is not native, an analysis of the trajectories does not reveal any evolution towards the native state, during that time. These results indicate that the distribution of protein conformations is multipeak shaped, so that apart from the peak corresponding to the native state, there are other peaks associated with average structures that are very different from the native and that can last as long as the native state. 相似文献
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F. Godlee 《BMJ (Clinical research ed.)》1994,309(6967):1491-1495
WHO says it has three main functions: to set normative standards; to provide technical advice and assistance on medical matters; and to advocate changes in health policy. During its 46 year history the first two functions have been a constant and uncontroversial backbone through which WHO has earned its reputation for scientific excellence. The third function, advocacy, came to the fore with the launch of Health for All in 1977, after which WHO took a key role in influencing international health policy. WHO''s friends and critics alike now say that the organisation is losing its influence and retreating into its technical and biomedical shell. This article maps the changes in WHO''s approach over the past 46 years and considers whether fears about its loss of influence are justified. 相似文献
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In raising the question "What is Cryptosporidium?", we aim to emphasize a growing need to re-evaluate the affinities of Cryptosporidium species within the phylum Apicomplexa so as to better understand the biology and ecology of these parasites. Here, we have compiled evidence from a variety of molecular and biological studies to build a convincing case for distancing Cryptosporidium species from the coccidia conceptually, biologically and taxonomically. We suggest that Cryptosporidium species must no longer be considered unusual or unique coccidia but rather seen for what they are--a distantly related lineage of apicomplexan parasites that are not in fact coccidia but that do occupy many of the same ecological niches. Looking at Cryptosporidium species without traditional coccidian blinders is likely to reveal new avenues of investigation into pathogenesis, epidemiology, treatment and control of these ubiquitous pathogens. 相似文献
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Yukihiro Morimoto 《Landscape and Ecological Engineering》2011,7(2):163-171
In recent times, there has been an increasing awareness of the traditional Japanese rural landscape, or Satoyama. Satoyama
is observed to provide a “backyard” for rice paddies, to accommodate biodiversity hotspots, to act as a model of sustainable
ecosystem management, and it represents Japan’s beautiful ancestral homeland. However, land-use changes, underuse of Satoyama,
and non-ecological infrastructures have degraded the abovementioned qualities in recent decades. As the significance of the
concept of Satoyama for a sustainable society is increasingly becoming clear, several movements have emerged, including the
Satoyama Initiative by the government of Japan, and the Japan Sub Global Assessment led by the United Nations University’s
Institute of Advanced Studies. Satoyama represents a model of sustainable society that maximizes the use of ecosystem services,
which will also be helpful in an international context. 相似文献
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Nishiyama T Kuroda S Takiguchi E Nakamura T Hashimoto K Tsuzuranuki K Kawakami T Masuho Y Kohroki J 《Biochemical and biophysical research communications》2012,420(3):487-491
ASB2 proteins are E3 ubiquitin (Ub) ligases that ubiquitinate filamins. There are two ASB2 splice variants, ASB2α and ASB2β. ASB2β has a ubiquitin-binding motif (UIM) at the N-terminal region but ASB2α does not. Here, we provide the first evidence that ASB2β but not ASB2α is monoubiquitinated and that this monoubiquitination involves the UIM. Myc-tagged ASB2β and hemagglutinin (HA)-tagged Ub were co-expressed in HEK293 cells using the pCMV expression vector. Immunoprecipitation with an anti-Myc antibody followed by immunoblotting with anti-Myc and anti-HA antibodies showed an additional ASB2β protein band that had both a Myc and a HA tag. The molecular weight of this protein was larger than that of ASB2β, and the difference in molecular weight between these two proteins corresponded to the molecular weight of monoubiquitin, strongly implying that monoubiquitinated ASB2β is produced in cells. ASB2β with mutations in the UIM motif; either Glu·Asp·Glu27-29Ala·Ala·Ala mutations (ASB2β M1) or a Ser38Ala mutation, (ASB2β M2) were not monoubiquitinated, suggesting the importance of the UIM for ASB2β monoubiquitination. Furthermore, an ASB2β mutant that lacked a SOCS box (ASB2β ΔC) and did not show E3 Ub ligase activity was monoubiquitinated to the same extent as the wild-type ASB2β. In contrast, an ASB2β mutant that lacked the UIM-containing domain (ASB2β ΔN) was not monoubiquitinated. These results suggest that ASB2β but not ASB2α might be monoubiquitinated and that the ASB2β UIM motif, but not its E3 Ub ligase activity, plays a pivotal role in this monoubiquitination. 相似文献
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Current methods of prediction of protein conformation are reviewedand the algorithms on which they rely are presented. For non-homologousproteins and after cross-validation the reported methods exhibita probability index, i.e. the per cent of correctly predictedresidues per predicted residues, of 6365% with a standarddeviation of the order of 7% for three conformational stateshelix,ß-strand and coil. This present limitation in theaccuracy of predictions that use only the information of thelocal sequence can be related essentially to the effect of long-rangeinteractions specific for each protein family. The methods basedon sequence similarity can improve the accuracy of predictionby expressing explicitly the homology of the protein to be predictedwith proteins in the database. In these circumstances the probabilityindex can reach 87% with a standard deviation of 6.6%. Thisproperty can be used for modeling homologous proteins by aidingin amino acid sequence alignments. The prediction of the tertiarystructure of a protein is still limited to the case of modelinga structure based on the known three-dimensional structure ofa homologous protein. 相似文献
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Wolfram Hartung Angela Sauter Neil C. Turner Ian Fillery Hermann Heilmeier 《Plant and Soil》1996,184(1):105-110
Abscisic acid (ABA) was detected in aqueous extracts of a range of different soils, beneath a range of crops, pasture and forest species. Assuming that all the ABA is dissolved in the soil solution concentrations ranged from 0.6–2.8 nM. This is in the range which computer simulations predict is required in soils in order to prevent ABA release from the root hair zones of plant roots. The concentration of ABA in the soil solution was highest in acid soils and in soils with reduced moisture, and was lowest in moist, neutral and moderately alkaline soils. ABA in the soil solution of maize fields increased during the vegetative period. After incubation in soil for 72 h, radioactive ABA was degraded by 30–40%. Tetcyclacis, an inhibitor of the oxidative breakdown of ABA, completely prevented the degradation of ABA in the soil solution. Acid conditions and high salt concentrations significantly retarded ABA breakdown. 相似文献
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Ugo E. Pazzaglia Terenzio Congiu Marcella Marchese Carlo Dell’Orbo 《Cell and tissue research》2010,340(3):533-540
Cortex fractured surface and graded osmic maceration techniques were used to study the secretory activity of osteoblasts,
the transformation of osteoblast to osteocytes, and the structural organization of the matrix around the cells with scanning
electron microscopy (SEM). A specialized membrane differentiation at the base of the cell was observed with finger-like, flattened
processes which formed a diffuse meshwork. These findings suggested that this membrane differentiation below the cells had
not only functioned in transporting collagen through the membrane but also in orienting the fibrils once assembled. Thin ramifications
arose from the large and flat membrane foldings oriented perpendicular to the plane of the osteoblasts. This meshwork of fine
filaments could not be visualized with SEM because they were obscured within the matrix substance. Their 3-D structure, however,
should be similar to the canalicular system. The meshwork of large, flattened processes was no more evident in the cells which
had completed their transformation into osteocytes. 相似文献
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Eva Martini Evelyn Schneider Clemens Neufert Markus F. Neurath 《Cell cycle (Georgetown, Tex.)》2016,15(21):2875-2881
As an inhibitor of apoptosis (IAP) family member, Survivin is known for its role during regulation of apoptosis. More recently its function as a cell cycle regulator has become evident. Survivin was shown to play a pivotal role during embryonic development and is highly expressed in regenerative tissue as well as in many cancer types. We examined the function of Survivin during mouse intestinal organogenesis and in gut pathophysiology. We found high expression of Survivin in experimentally induced colon cancer in mice but also in colon tumors of humans. Moreover, Survivin was regulated by TGF-β and was found to be highly expressed during mucosal healing following intestinal inflammation. We identified that expression of Survivin is essential early on in life, as specific deletion of Survivin in Villin expressing cells led to embryonic death around day 12 post coitum. Together with our recent study on the role of Survivin in the gut of adult mice our data demonstrate that Survivin is an essential guardian of embryonic gut development and adult gut homeostasis protecting the epithelium from cell death promoting the proliferation of intestinal stem and progenitor cells. 相似文献
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We reviewed recent reports from administrative databases and clinical registries addressing the utilization of coronary artery bypass grafting (CABG) in Canada. The Canadian CABG rate per 100,000 people increased from 31.1 to 43.2 between 1981-82 and 1986-87. Between 1981 and 1986 the rate in the United States increased from 69.9 to 95.3 per 100,000, consistently about two times the Canadian rate. Provincial data have shown particular growth in utilization among elderly people. However, in the United States the 1985 CABG rate was twice as high as the aggregated age-specific rates for Ontario and Manitoba among people 65 to 74 years of age and four times higher among those 75 years or more. Limited registry data suggest that the Canadian CABG case mix is similar to the case mix in major US centres and that, utilization growth notwithstanding, the procedure is largely applied to patients who should, in theory, benefit (i.e., those with severe angina, impaired left ventricular function and left main-stem or triple-vessel disease). However, chart audits and registry evaluations using explicit criteria are needed to compare the use of CABG in Canada and the United States. In addition, Canadian data show moderate regional and municipal variations, the 1986-87 rates per 100,000 population in major census metropolitan areas varying from 19.5 to 46.9. Areas with consistently low rates raise particular concerns about impaired access to CABG. Reasons for variations should therefore be a research priority. 相似文献
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Lieven Therry Andrzej Zawal Dries Bonte Robby Stoks 《Biological journal of the Linnean Society. Linnean Society of London》2014,112(3):556-568
Individuals at the expansion front during a climate‐driven range expansion are expected to differ phenotypically from those individuals in core populations. Little information is known about the joint, potentially opposing, effects of stressful conditions at the range edge versus evolutionary changes that take place during range expansion in shaping the phenotypes at the range front. We investigated the effect of range expansion on immune function, body condition and flight‐related morphology (flight muscle ratio, wing loading, and wing aspect ratio) of field‐collected females of the poleward‐moving damselfly Coenagrion scitulum. Individuals at the expansion front had a lower body condition, which indicated more stressful conditions at the range edge. Despite the counteracting effect of the shorter growth season, the higher flight muscle ratios at the expansion front indicated a strong selection for dispersal ability during range expansion. The current study suggests that models need to incorporate the interplay of stressful conditions and evolutionary processes at the expansion front to arrive at robust predictions of future species distributions under global warming. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 556–568. 相似文献