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排序方式: 共有211条查询结果,搜索用时 156 毫秒
91.
We describe the design and the Fmoc/tBu solid phase synthesis of a 20 residue long peptide containing five regularly distributed lysines. Cyclization of this peptide was achieved using BOP as coupling agent. After side-chain deprotection, all the basic residues were iodoacetylated and then allowed to react either with a C-terminal free COOH peptide or with peptides bearing a cysteamide group. The final pentameric templates were identified by mass and amino acid analysis which gave data compatible with the expected values. 相似文献
92.
S Corradin J Mau?l A Ransijn C Stürzinger G Vergères 《The Journal of biological chemistry》1999,274(24):16782-16787
Leishmania, a protozoan parasite of macrophages, has been shown to interfere with host cell signal transduction pathways including protein kinase C (PKC)-dependent signaling. Myristoylated alanine-rich C kinase substrate (MARCKS) and MARCKS-related protein (MRP, MacMARCKS) are PKC substrates in diverse cell types. MARCKS and MRP are thought to regulate the actin network and thereby participate in cellular responses involving cytoskeletal rearrangement. Because MRP is a major PKC substrate in macrophages, we examined its expression in response to infection by Leishmania. Activation of murine macrophages by cytokines increased MRP expression as determined by Western blot analysis. Infection with Leishmania promastigotes at the time of activation or up to 48 h postactivation strongly decreased MRP levels. Leishmania-dependent MRP depletion was confirmed by [3H]myristate labeling and by immunofluorescence microscopy. All species or strains of Leishmania parasites tested, including lipophosphoglycan-deficient Leishmania major L119, decreased MRP levels. MRP depletion was not obtained with other phagocytic stimuli including zymosan, latex beads, or heat-killed Streptococcus mitis, a Gram-positive bacterium. Experiments with [3H]myristate labeled proteins revealed the appearance of lower molecular weight fragments in Leishmania-infected cells suggesting that MRP depletion may be due to proteolytic degradation. 相似文献
93.
Phagocytosis of Leishmania enhances macrophage activation by IFN-gamma and lipopolysaccharide 总被引:5,自引:0,他引:5
This investigation describes the ability of Leishmania promastigotes to enhance activation of bone marrow-derived murine macrophages in vitro if added together with rIFN-gamma in the presence or absence of LPS. Activation was defined as the capacity for arginine-derived NO2- production and the killing of intracellular Leishmania. Enhanced NO2- production was observed for either CBA or C3H/HeJ macrophages undergoing phagocytosis at the time of activation. Other phagocytic stimuli including inert polystyrene latex beads were as effective as Leishmania. No correlation could be demonstrated between the enhanced NO2- release and secretion of products of the respiratory burst or PGE2. However, TNF-alpha secretion was elevated in cultures undergoing phagocytosis and a relationship between hexosemonophosphate shunt activity and NO2- levels was evident. These studies confirm and extend previous reports that phagocytosis plays an important role in the regulation of macrophage physiology. 相似文献
94.
Marcus Mau Karl‐Heinz Südekum Achim Johann Alexander Sliwa Thomas M. Kaiser 《American journal of primatology》2009,71(8):663-669
Gelada baboons are the sole survivors of the genus Theropithecus and the only known graminivorous primates. They developed special adaptations to their diet such as high‐crowned teeth for processing hard and abrasive feed. The fine‐tuning of salivary protein composition might be another key mechanism that is used by species for adapting to the environment and competing with rivals for exploiting new ecological niches. In order to test whether gelada (graminivorous) and hamadryas baboons (omnivorous) differ in their salivary protein composition, we compared whole saliva samples of captive Theropithecus gelada and Papio hamadryas using gel electrophoresis and tannin‐binding assay. We hypothesized that the amount of proline‐rich salivary proteins with tannin‐binding capacity is higher in baboons consuming a feed with high dicot/monocot rations. Dicots produce tannins as a chemical defense system, discouraging animals from eating them. In contrast to dicots, monocots do not synthesize tannins. The presence of tannin‐binding proteins in saliva should effectively inactivate the dicot tannin‐based defense mechanism and increase the dietary breadth and/or the capability to switch between monocots and dicot leaves. The lack of such tannin‐binding proteins in saliva would indicate a narrow dietary spectrum more restricted to monocots. We found T. gelada to completely lack proline‐rich proteins (PRPs) and tannin‐binding capacity similar to a great variety of other grazing mammals. In contrast, P. hamadryas does possess PRPs with tannin‐binding activity. The findings support a growing body of evidence suggesting a high‐level specialization of T. gelada to grass diets. However, it remains unclear, whether loss of salivary tannin‐binding capacity drove the gelada into its narrow feeding niche, or whether this loss is the result of a long process of increased specialization. Thus, from an ecological point of view, T. gelada appears to be more vulnerable to environmental changes than other baboon species owing to its narrow dietary traits. Am. J. Primatol. 71:663–669, 2009. © 2009 Wiley‐Liss, Inc. 相似文献
95.
Nicholas Fisichelli Alexandra Wright Karen Rice Alida Mau Cindy Buschena Peter B. Reich 《Oikos》2014,123(11):1331-1340
Species will respond individually to climate change and this poses a challenge for modeling climate–vegetation dynamics using broader taxonomic or biogeographical classifications. Additionally, responses to climate and environmental conditions may shift with ontogeny, further complicating efforts to understand the likely rates and directions of vegetation change. We measured emergence, leaf‐out rate, growth, and survival of first‐year seedlings in response to warming, precipitation regime shifts, and seedbed condition (leaf litter presence/absence). We grouped species into three levels of organization (species‐specific, biome‐level and broad taxonomic group) and hypothesized that most metrics of seedling performance would be best described by species‐specific models, as even similar species may respond in vastly different ways to global change. Results showed that the species‐specific model was the best fit for emergence and development rates, whereas growth and survival could be captured through broader groupings, with the broadleaf temperate group exhibiting the greatest growth and conifers the shortest survival times. The sign and magnitude of response to climate and seedbed condition varied with treatment combinations and metric of performance. For example, seedlings grew more in response to warming, but conditions too dry or too wet limited this positive response. Also, warmer temperatures generally increased emergence, development, and growth, but decreased survival, whereas leaf litter presence decreased emergence and slowed development, but increased survival. The results presented here are for first‐year seedlings and in many cases the responses are different from other studies using older plants. Future research and climate vegetation modeling needs to assess performance at multiple development stages and determine where key bottleneck phases for population growth occur for individual species. 相似文献
96.
97.
Ma S Tang KH Chan YP Lee TK Kwan PS Castilho A Ng I Man K Wong N To KF Zheng BJ Lai PB Lo CM Chan KW Guan XY 《Cell Stem Cell》2010,7(6):694-707
A novel paradigm in tumor biology suggests that cancer growth is driven by stem-like cells within a tumor, called tumor-initiating cells (TICs) or cancer stem cells (CSCs). Here we describe the identification and characterization of such cells from hepatocellular carcinoma (HCC) using the marker CD133. CD133 accounts for approximately 1.3%-13.6% of the cells in the bulk tumor of human primary HCC samples. When compared with their CD133? counterparts, CD133(+) cells not only possess the preferential ability to form undifferentiated tumor spheroids in vitro but also express an enhanced level of stem cell-associated genes, have a greater ability to form tumors when implanted orthotopically in immunodeficient mice, and can be serially passaged into secondary animal recipients. Xenografts resemble the original human tumor and maintain a similar percentage of tumorigenic CD133(+) cells. Quantitative PCR analysis of 41 separate HCC tissue specimens with follow-up data found that CD133(+) tumor cells were frequently detected at low quantities in HCC, and their presence was also associated with worse overall survival and higher recurrence rates. Subsequent differential microRNA expression profiling of CD133(+) and CD133? cells from human HCC clinical specimens and cell lines identified an overexpression of miR-130b in CD133(+) TICs. Functional studies on miR-130b lentiviral-transduced CD133? cells demonstrated superior resistance to chemotherapeutic agents, enhanced tumorigenicity in vivo, and a greater potential for self renewal. Conversely, antagonizing miR-130b in CD133(+) TICs yielded an opposing effect. The increased miR-130b paralleled the reduced TP53INP1, a known miR-130b target. Silencing TP53INP1 in CD133? cells enhanced both self renewal and tumorigenicity in vivo. Collectively, miR-130b regulates CD133(+) liver TICs, in part, via silencing TP53INP1. 相似文献
98.
M. Mau K.‐H. Südekum A. Johann A. Sliwa T.M. Kaiser 《Journal of medical primatology》2010,39(3):187-190
Background Little is known about salivary α‐amylase expression in primates. Methods We compared saliva of gelada and hamadryas baboons, chimpanzees and humans using SDS‐PAGE and immunoblotting. Results and conclusions Amylase expression was increased in hamadryas baboons (P = 0.0376) compared to humans and might indicate dietary starch use in Cercopithecines. 相似文献
99.
Roger I. Vargas Jaime C. Piñero Ronald F. L. Mau John D. Stark Mark Hertlein Agenor Mafra‐Neto Reginald Coler Anna Getchell 《Entomologia Experimentalis et Applicata》2009,131(3):286-293
Studies were conducted in 2007 and 2008 in Hawaii, USA to quantify attraction and feeding responses resulting in mortality of the male oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), to a novel male annihilation treatment (MAT) formulation consisting of specialized pheromone and lure application technology (SPLAT) in combination with methyl eugenol (ME) and spinosad (=SPLAT‐MAT‐ME with spinosad) in comparison with Min‐U‐Gel‐ME with naled (Dibrom). Our approach involved a novel behavioral methodology for evaluation of slow‐acting reduced‐risk insecticides. Methyl eugenol treatments were weathered for 1, 2, 4, and 8 weeks in California, USA, and shipped to Hawaii for bioassays. In field tests involving bucket traps to attract and capture wild males, and in toxicity studies conducted in 1 m3 cages using released males of controlled ages, SPLAT‐MAT‐ME with spinosad performed similar to or outperformed the standard formulation of Min‐U‐Gel‐ME with naled for material aged for up to 8 weeks in the 2008 tests. In laboratory feeding tests in which individual males were exposed for 5 min to the different ME treatments, mortality induced by SPLAT‐MAT‐ME with spinosad recorded at 24 h did not differ from that caused by Min‐U‐Gel ME with naled at 1, 2, and 4 weeks. Spinosad has low contact toxicity, and when mixed with SPLAT offers a reduced‐risk alternative for control of B. dorsalis, without many of the negative effects to humans and non‐targets of broad‐spectrum contact poisons such as naled. Our results indicate that SPLAT‐MAT‐ME with spinosad offers potential for control of males in an area‐wide integrated pest management (IPM) system without the need for conventional organophosphates. 相似文献
100.
Ishfaq Ahmed Sheikh Amit Kumar Singh Nagendra Singh Mau Sinha S. Baskar Singh Asha Bhushan Punit Kaur Alagiri Srinivasan Sujata Sharma Tej P. Singh 《The Journal of biological chemistry》2009,284(22):14849-14856
The crystal structure of the complex of lactoperoxidase (LPO) with its
physiological substrate thiocyanate (SCN–) has been
determined at 2.4Å resolution. It revealed that the
SCN– ion is bound to LPO in the distal heme cavity. The
observed orientation of the SCN– ion shows that the sulfur
atom is closer to the heme iron than the nitrogen atom. The nitrogen atom of
SCN– forms a hydrogen bond with a water (Wat) molecule at
position 6′. This water molecule is stabilized by two hydrogen bonds
with Gln423 Nε2 and Phe422 oxygen. In
contrast, the placement of the SCN– ion in the structure of
myeloperoxidase (MPO) occurs with an opposite orientation, in which the
nitrogen atom is closer to the heme iron than the sulfur atom. The site
corresponding to the positions of Gln423, Phe422 oxygen,
and Wat6′ in LPO is occupied primarily by the side chain of
Phe407 in MPO due to an entirely different conformation of the loop
corresponding to the segment Arg418–Phe431 of LPO.
This arrangement in MPO does not favor a similar orientation of the
SCN– ion. The orientation of the catalytic product
OSCN– as reported in the structure of
LPO·OSCN– is similar to the orientation of
SCN– in the structure of LPO·SCN–.
Similarly, in the structure of
LPO·SCN–·CN–, in which
CN– binds at Wat1, the position and orientation of
the SCN– ion are also identical to that observed in the
structure of LPO·SCN.Lactoperoxidase
(LPO4; EC 1.11.1.7) is
a Fe3+ heme enzyme that belongs to the mammalian peroxidase family
(1). The family of mammalian
peroxidases comprises lactoperoxidase
(2), eosinophil peroxidase
(3), thyroid peroxidase
(4), and myeloperoxidase (MPO)
(5). LPO, eosinophil
peroxidase, and MPO are responsible for antimicrobial function and innate
immune responses
(6–8),
whereas thyroid peroxidase plays a key role in thyroid hormone biosynthesis
(9). These peroxidases are
different from plant and fungal peroxidases because unlike plant and fungal
enzymes, the prosthetic heme group in mammalian peroxidases is covalently
linked to the protein (10).
There are also several striking structural and functional differences among
the mammalian peroxidases
(11). The heme group in MPO is
attached to the protein via three covalent linkages
(12), whereas LPO
(12,
13), eosinophil peroxidase
(12), and thyroid peroxidase
(12) contain only two ester
linkages. These covalent and various non-covalent linkages contribute
differentially to the high stability of the heme core as well as for the
peculiar values of their redox potentials
(2,
14). Furthermore, MPO consists
of two disulfide-linked protein chains, whereas LPO, eosinophil peroxidase,
and thyroid peroxidase are single chain proteins, although their chain lengths
differ greatly. In addition, their sequences contain several critical amino
acid differences that may also contribute to the variations in the
stereochemical environments of the substrate-binding sites. As a consequence
of these differences, the mammalian enzymes oxidize various inorganic ions
such as SCN–, Br–, Cl–, and
I– with differing specificities and potencies. Biochemical
studies have shown that LPO catalyzes preferentially the conversion of
SCN– to OSCN–
(15,
16), whereas MPO uses halides
(17,
18) with a preference for
chloride ion as the substrate. The preferences of eosinophil peroxidase and
thyroid peroxidase are bromide and iodide, respectively. However, the
stereochemical basis of the reported preferences for the substrates by
mammalian heme peroxidases is still unclear. So far, the structures of only
two mammalian enzymes, MPO and LPO, have been determined
(12,
13). It is of considerable
importance to identify the structural parameters that are responsible for the
subtle specificities. In the present work, we have attempted to address this
question through the new crystal structures of LPO complexes with
SCN– ions using goat, bovine, and buffalo lactoperoxidases.
Because the overall structures of complexes of SCN– with LPO
from all three species were found to be identical, the structure of the
complex of buffalo LPO with SCN– and the ternary complex with
SCN– and CN– will be discussed here, and
buffalo LPO will be termed hereafter as LPO. To highlight the factors
pertaining to binding specificity of SCN–, a comparison of
the structures of LPO·SCN– and
MPO·SCN– has also been made, revealing many valuable
differences pertaining to the observed orientations of the common substrate,
SCN– ion, when bound at the substrate-binding site in the
distal heme cavity of the two structures. The structures of
LPO·SCN– and MPO·SCN– clearly
show that the bound SCN– ions are present in the distal heme
cavity of two enzymes with opposite orientations. In the structure of
LPO·SCN–, the sulfur atom is closer to the heme iron
than the nitrogen atom, whereas in that of MPO·SCN–,
the nitrogen atom is closer to the heme iron than the sulfur atom. As a result
of this, the interactions of the SCN– ion in the distal site
of two proteins differ drastically. Gln423, a conserved water (Wat)
molecule at position 6′, and a well aligned carbonyl oxygen of
Phe422 in the proximity of the substrate-binding site in LPO
against a protruding Phe407 in MPO seem to play the key roles in
inducing the observed orientations of SCN– ions in LPO and
MPO. The structure of LPO·SCN– has also been compared
with the structure of its ternary complex with SCN– and
CN– ions. 相似文献