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931.
932.
Microtubules are versatile cellular polymers that play a role in cell shape determination and mediate various motile processes such as ciliary and flagellar bending, chromosome movements and organelle transport. That a sliding microtubule mechanism can generate force has been demonstrated in highly ordered structures such as axonemes, and microtubule-based force generation almost certainly contributes to the function of mitotic and meiotic spindles. Most cytoplasmic microtubule arrays, however, do not exhibit the structural regularity of axonemes and some spindles, and often appear disorganized. Yet many cellular activities (such as shape changes during morphogenesis, axonal extension and spindle assembly) involve highly coordinated microtubule behaviour and possibly require force generated by an intermicrotubule sliding mechanism, or perhaps use sliding to move microtubules rapidly into a protrusion for stabilization. Here we show that active sliding between cytoplasmic microtubules can occur in microtubule bundles of the amoeba Reticulomyxa. A force-producing mechanism of this sort could be used by this organism to facilitate the extension of cell processes and to generate the dynamic movements of the cytoplasmic network. 相似文献
933.
934.
Leers MP Björklund V Björklund B Jörnvall H Nap M 《Cellular and molecular life sciences : CMLS》2002,59(8):1358-1365
We investigated the distribution and fate of apoptotic bodies during human development and in the adult, using an antibody
(M30) that recognizes a neo-epitope formed early in the apoptotic cascade by caspase cleavage of cytokeratin 18. In the fetus,
we found extensive accumulation of M30-positive, non-phagocytosed fragments in the red pulp of the spleen, subcutaneous and
submucosal vessels, the interstitium of the lung, and the glomerular mesangium of the kidneys. In the liver, M30-immunoreactive
fragments were found inside macrophages in the sinusoids. The number of these fragments and the intensity of the immunostaining
increased with the gestational age of the fetus. In the adult, M30-positive fragments were barely detectable in normal tissues.
However, many pathological situations, including both chronic degenerative processes and metastatic cancer, were associated
with accumulation of M30-positive fragments in the red pulp of the spleen. In the liver and kidney, no fragments could be
detected. Remarkably, 13 of the 16 patients with metastasized cancer showed pronounced accumulation of M30-positive fragments
containing hematoxylin-reactive material in the red pulp of the spleen. In the non-cancerous cases, such DNA-containing fragments
were only seen in 9 of 94 cases. The results show that when apoptotic activity is high, as during development in the fetus
or during metastasis and other pathological processes in the adult, the phagocytic clearance of apoptotic bodies can be overloaded.
These apoptotic fragments then accumulate in the spleen. The visual detection of apoptotic fragments is concluded to reflect
increased cell turnover.
Received 1 July 2002; accepted 1 July 2002 相似文献
935.
Peptide aptamers have emerged as powerful new tools for molecular medicine. They can specifically bind to and functionally
inactivate a given target molecule under intracellular conditions. Typically, peptide aptamers are generated by screening
a randomized peptide expression library, displayed from the Escherichia coli thioredoxin A (TrxA) protein. Here, we transferred peptide moieties from defined TrxA-based peptide aptamers to alternative
scaffold proteins, such as the green fluorescent protein and staphylococcal nuclease. Yeast and mammalian two-hybrid assays
as well as in vitro binding analyses show that the TrxA scaffold can be a major determinant for the binding of peptide aptamers.
In addition, we demonstrate that TrxA can correctly display peptide sequences that correspond to the binding domains of natural
interaction partners. Therefore, sequence analyses of TrxA-based peptide aptamers, isolated by two-hybrid screening from randomized
expression libraries, should also be useful to find cellular binding partners for a given target protein, by homology.
Received 1 August 2002; received after revision 17 September 2002; accepted 19 September 2002
RID="*"
ID="*"Corresponding author. 相似文献
936.
Strömberg P Svensson S Hedberg JJ Nordling E Höög JO 《Cellular and molecular life sciences : CMLS》2002,59(3):552-559
The human alcohol dehydrogenase system is comprised of multiple forms that catalyse the oxidation/reduction of a large variety of alcohols and aldehydes. A transition that results in an Ile308Val substitution was identified in the human ADH2 gene by single-strand conformation polymorphism analysis. Screening a Swedish population revealed that Val308 was the most frequent allele (73%), and site-directed mutagenesis was used to obtain both allelozymes, which were expressed in Escherichia coli for characterisation. Thermostability was assayed by activity measurements and circular dichroism spectroscopy. The results showed that the 308Val substitution decreases protein stability, as compared to the Ile308 variant, an effect also demonstrated during prolonged storage. Ethanol, octanol, 12-hydroxydodecanoic acid and all-trans retinol were used as model substrates and, generally, slightly higher Km values were observed with Val at position 308. Finally, homology modelling, from mouse ADH2, further supported the decreased stability of the Val308 variant and located position 308 in the subunit interface of the molecule and in the vicinity of the active-site pocket entrance. In conclusion, the Ile308Val substitution represents a novel functional polymorphism within the human alcohol dehydrogenase gene cluster that may affect the metabolism of ethanol and other substrates. 相似文献
937.
Screening for differentially expressed genes is a straightforward approach to study the molecular basis for changes in gene
expression. Differential display analysis has been used by investigators in diverse fields of research since it was developed.
Differential display has also been the approach of choice to investigate changes in gene expression in response to various
biological challenges in invertebrates. We review the application of differential display analysis of gene expression in invertebrates,
and provide a specific example using this technique for novel gene discovery in the nematode Caenorhabditis elegans. 相似文献
938.
Morphine 6 glucuronide stimulates nitric oxide release in mussel neural tissues: evidence for a morphine 6 glucuronide opiate receptor subtype 总被引:1,自引:0,他引:1
Mantione K Zhu W Rialas C Casares F Cadet P Franklin AL Tonnesen J Stefano GB 《Cellular and molecular life sciences : CMLS》2002,59(3):570-574
We have previously demonstrated that Mytilus edulis pedal ganglia contain opiate alkaloids, i.e., morphine and morphine 6 glucuronide (M6G), as well as mu opiate receptor subtype
fragments exhibiting high sequence similarity to those found in mammals. Now we demonstrate that M6G stimulates pedal ganglia
constitutive nitric oxide (NO) synthase (cNOS)-derived NO release at identical concentrations and to similar peak levels as
morphine. However, the classic opiate antagonist, naloxone, only blocked the ability of morphine to stimulate cNOS-derived
NO release and not that of M6G. CTOP, a mu-specific antagonist, blocked the ability of M6G to induce cNOS-derived NO release
as well as that of morphine, suggesting that a novel mu opiate receptor was present and selective toward M6G. In examining
a receptor displacement analysis, both opiate alkaloids displaced [3H]-dihydromorphine binding to the mu opiate receptor subtype. However, morphine exhibited a twofold higher affinity, again
suggesting that a novel mu opiate receptor may be present.
Received 1 November 2001; received after revision 1 February 2002; accepted 1 February 2002 相似文献
939.
Microbial cycling of volatile organic sulfur compounds 总被引:7,自引:0,他引:7
Lomans BP van der Drift C Pol A Op den Camp HJ 《Cellular and molecular life sciences : CMLS》2002,59(4):575-588
Microbial cycling of volatile organic sulfur compounds (VOSCs), especially dimethyl sulfide (DMS) and methanethiol (MT), is intensively studied because these compounds play an important role in the processes of global warming, acid precipitation, and the global sulfur cycle. VOSC concentrations in freshwater sediments are low due to the balance between the formation and degradation of these compounds. These reactions occur for the greater part at the oxic/anoxic interphase of sediment and water column. In contrast to marine ecosystems, where dimethylsulfoniopropionate is the main precursor of MT and DMS, in freshwater ecosystems, VOSCs are formed mainly by methylation of sulfide and to a lesser extent from the degradation of S-containing amino acids. One of the major routes for DMS and MT formation through sulfide methylation is anaerobic O-demethylation of methoxylated aromatic compounds. Inhibition studies have revealed that the major part of the endogenously produced MT and DMS is degraded anaerobically by methanogens. The major bacterial groups involved in formation and consumption of VOSCs are described. 相似文献
940.
Wabnitz H Bittner L de Castro AR Döhrmann R Gürtler P Laarmann T Laasch W Schulz J Swiderski A von Haeften K Möller T Faatz B Fateev A Feldhaus J Gerth C Hahn U Saldin E Schneidmiller E Sytchev K Tiedtke K Treusch R Yurkov M 《Nature》2002,420(6915):482-485
Intense radiation from lasers has opened up many new areas of research in physics and chemistry, and has revolutionized optical technology. So far, most work in the field of nonlinear processes has been restricted to infrared, visible and ultraviolet light, although progress in the development of X-ray lasers has been made recently. With the advent of a free-electron laser in the soft-X-ray regime below 100 nm wavelength, a new light source is now available for experiments with intense, short-wavelength radiation that could be used to obtain deeper insights into the structure of matter. Other free-electron sources with even shorter wavelengths are planned for the future. Here we present initial results from a study of the interaction of soft X-ray radiation, generated by a free-electron laser, with Xe atoms and clusters. We find that, whereas Xe atoms become only singly ionized by the absorption of single photons, absorption in clusters is strongly enhanced. On average, each atom in large clusters absorbs up to 400 eV, corresponding to 30 photons. We suggest that the clusters are heated up and electrons are emitted after acquiring sufficient energy. The clusters finally disintegrate completely by Coulomb explosion. 相似文献