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121.
Kad NM Rovner AS Fagnant PM Joel PB Kennedy GG Patlak JB Warshaw DM Trybus KM 《The Journal of cell biology》2003,162(3):481-488
Each of the heads of the motor protein myosin II is capable of supporting motion. A previous report showed that double-headed myosin generates twice the displacement of single-headed myosin (Tyska, M.J., D.E. Dupuis, W.H. Guilford, J.B. Patlak, G.S. Waller, K.M. Trybus, D.M. Warshaw, and S. Lowey. 1999. Proc. Natl. Acad. Sci. USA. 96:4402-4407). To determine the role of the second head, we expressed a smooth muscle heterodimeric heavy meromyosin (HMM) with one wild-type head, and the other locked in a weak actin-binding state by introducing a point mutation in switch II (E470A). Homodimeric E470A HMM did not support in vitro motility, and only slowly hydrolyzed MgATP. Optical trap measurements revealed that the heterodimer generated unitary displacements of 10.4 nm, strikingly similar to wild-type HMM (10.2 nm) and approximately twice that of single-headed subfragment-1 (4.4 nm). These data show that a double-headed molecule can achieve a working stroke of approximately 10 nm with only one active head and an inactive weak-binding partner. We propose that the second head optimizes the orientation and/or stabilizes the structure of the motion-generating head, thereby resulting in maximum displacement. 相似文献
122.
Long and short term variations in suspended particulate material: the influence on light available to the phytoplankton community 总被引:7,自引:1,他引:6
The magnitude and frequency of events leading to changes in turbidity have been studied in a large (61 km2), shallow (mean depth 3.4 m) wind-exposed lake basin at the western end of Lake Mälaren, Sweden. In this paper we couple changes in suspended particulate inorganic material (SPIM) resulting from wind driven sediment resuspension, and variations in the discharge and sediment load, to spectral variations in subsurface light and estimates of photosynthetically active radiation (PAR). To accomplish this we use a semi-analytical model which predicts the spectral variations in downwelling irradiance (E
d()) and the attenuation coefficient of downwelling irradiance (K
d()), as a function of the concentrations of chlorophyll, dissolved yellow substances, and suspended inorganic and organic particulate material. Unusually high river discharge, led to large inputs of yellow substances and large in lake yellow substance concentrations (a
ys(420) 20 m–1), causing variations in yellow substance concentration to have the greatest role in influencing temporal trends in the attenuation of PAR and variations in the depth of the euphotic zone (Z
eup). In spite of this, variations in SPIM could account for approximately 60% of the variation in Z
eup attributed to changes in yellow substances alone. Our results show that changes in suspended sediment concentration leads to both long-term and short-term changes in the attenuation of PAR, even in the presence of high concentrations of dissolved yellow substances. 相似文献
123.
Yoshie Matsuda Genqing Liang Yali Zhu Fengshan Ma Richard S. Nelson Biao Ding 《Protoplasma》2002,220(1-2):0051-0058
Summary. Previous work has demonstrated that some endogenous plant gene promoters are active in selective companion cells of the phloem,
depending on organ types and developmental stages. Here we report that the Commelina yellow mottle virus (CoYMV) promoter
is active in the companion cells of leaves, stems and roots of transgenic Nicotiana tabacum cv. Xanthi NN, using β-glucuronidase (GUS) as a reporter. Thus, the CoYMV promoter has a broad organ specificity. This promoter
can be useful in molecular studies on the functions of companion cells in many aspects of phloem biology, such as regulation
of long-distance transport, macromolecular traffic, plant development and interaction with pathogens. It may also be useful
in engineering crops that produce specific gene products in the companion cells to block long-distance movement of pathogens.
Received February 5, 2002; accepted March 27, 2002; published online July 4, 2002
RID="*"
ID="*" Correspondence and reprints: Department of Plant Biology and Plant Biotechnology Center, 207 Rightmire Hall, Ohio State
University, 1060 Carmack Road, Columbus, OH 43210, U.S.A. 相似文献
124.
125.
Plant research is moving into the post-genomic era. Proteomic-based strategies are now being developed to study functional aspects of the genes predicted from the various genome-sequencing initiatives. All biological processes depend on interactions formed between proteins and the mapping of such interactions on a global scale is providing interesting functional insights. One of the techniques that has proved itself invaluable in the mapping of protein-protein interactions is the yeast two-hybrid system. This system is a sensitive molecular genetic approach for studying protein-protein interactions in vivo. In this review we will introduce the yeast two-hybrid system, discuss modifications of the system that may be of interest to the plant science community and suggest potential applications of the technology. 相似文献
126.
Photoactive yellow protein (PYP) is a prototype of the PAS domain superfamily of signaling proteins. The signaling process
is coupled to a three-state photocycle. After the photoinduced trans-cis isomerization of the chromophore, 4-hydroxycinnamic acid (pCA), an early intermediate (pR) is formed, which proceeds to a
second intermediate state (pB) on a sub-millisecond time scale. The signaling process is thought to be connected to the conformational
changes upon the formation of pB and its recovery to the ground state (pG), but the exact signaling mechanism is not known.
Experimental studies of PYP by solution NMR and X-ray crystallography suggest a very flexible protein backbone in the ground
as well as in the signaling state. The relaxation from the pR to the pB state is accompanied by the protonation of the chromophore's
phenoxyl group. This was found to be of crucial importance for the relaxation process. With the goal of gaining a better understanding
of these experimental observations on an atomistic level, we performed five MD simulations on the three different states of
PYP: a 1 ns simulation of PYP in its ground state [pG(MD)], a 1 ns simulation of the pR state [pR(MD)], a 2 ns simulation
of the pR state with the chromophore protonated (pRprot), a 2 ns simulation of the pR state with Glu46 exchanged by Gln (pRGln)
and a 2 ns simulation of PYP in its signaling state [pB(MD)]. Comparison of the pG simulation results with X-ray and NMR data,
and with the results obtained for the pB simulation, confirmed the experimental observations of a rather flexible protein
backbone and conformational changes during the recovery of the pG from the pB state. The conformational changes in the region
around the chromophore pocket in the pR state were found to be crucially dependent on the strength of the Glu46-pCA hydrogen
bond, which restricts the mobility of the chromophore in its unprotonated form considerably. Both the mutation of Glu46 with
Gln and the protonation of the chromophore weaken this hydrogen bond, leading to an increased mobility of pCA and large structural
changes in its surroundings. These changes, however, differ considerably during the pRGln and pRprot simulations, providing
an atomistic explanation for the enhancement of the rate constant in the Gln46 mutant.
Electronic supplementary material to this article is available at and is accessible for athorized users.
Electronic Publication 相似文献
127.
Molecular dynamics simulation techniques, together with semiempirical PM3 calculations, have been used to investigate the effect of photoisomerization of the 4-hydroxy-cinnamic acid chromophore on the structural properties of the photoactive yellow protein (PYP) from Ectothiorodospira halophila. In this bacteria, exposure to blue light leads to a negative photoactic response. The calculations suggest that the isomerization does not directly destabilize the protein. However, because of the isomerization, a proton transfer from a glutamic acid residue (Glu46) to the phenolate oxygen atom of the chromophore becomes energetically favorable. The proton transfer initiates conformational changes within the protein, which are in turn believed to lead to signaling. 相似文献
128.
So Nishikawa Kazuaki Homma Yasunori Komori Mitsuhiro Iwaki Tetsuichi Wazawa Atsuko Hikikoshi Iwane Junya Saito Reiko Ikebe Eisaku Katayama Toshio Yanagida Mitsuo Ikebe 《Biochemical and biophysical research communications》2002,290(1):311-317
Among a superfamily of myosin, class VI myosin moves actin filaments backwards. Here we show that myosin VI moves processively on actin filaments backwards with large ( approximately 36 nm) steps, nevertheless it has an extremely short neck domain. Myosin V also moves processively with large ( approximately 36 nm) steps and it is believed that myosin V strides along the actin helical repeat with its elongated neck domain that is critical for its processive movement with large steps. Myosin VI having a short neck cannot take this scenario. We found by electron microscopy that myosin VI cooperatively binds to an actin filament at approximately 36 nm intervals in the presence of ATP, raising a hypothesis that the binding of myosin VI evokes "hot spots" on actin filaments that attract myosin heads. Myosin VI may step on these "hot spots" on actin filaments in every helical pitch, thus producing processive movement with 36 nm steps. 相似文献
129.
We measured the effect of the intercalating oxazole yellow DNA dye quinolinium,4-[(3-methyl-2(3H)-benzoxazolylidene)methyl]-1-[3-(trimethylammonio)propyl]-,diiodide (YO-PRO) and its homodimer (YOYO) on the melting of self-complementary DNA duplexes using a gel-based assay. The assay, which requires a self-complementary DNA sequence, is independent of the optical properties of the molecules in solution. The melting temperature of the DNA is observed to increase in direct proportion to the number of occupied intercalation sites on the DNA, irrespective of whether the dye molecules are in monomer or dimer form. The increase is approximately 2.5 degrees C for each intercalation site occupied in the presence of 38 mM [Na(+)], for dye/duplex ratios in which less than 1/5 of the available intercalation sites are occupied. 相似文献
130.
Hall MJ Hutchinson RA Farkas R Adams ZJ Wyatt NP 《Medical and veterinary entomology》2003,17(3):280-287
The Lucitrap (Miazma Pty Ltd, Queensland, Australia) combined with a synthetic odour bait, Lucilure (Miazma Pty Ltd, Queensland, Australia), is a commercially available trap for sampling and control of Lucilia cuprina (Wiedemann) in Australia. It was tested in Hungary against Lucilia sericata (Meigen) (Diptera: Calliphoridae), a cause of sheep strike throughout temperate Europe. The standard Lucitrap was tested against black or yellow sticky target traps. Both trap types were baited with either Lucilure or liver and 10% w/v sodium sulphide solution. With Lucilure as bait, L. sericata were caught on sticky traps but not in Lucitraps. With liver and sodium sulphide as bait, sticky traps caught 500-1500 times more L. sericata than Lucitraps. An adhesive sheet fitted to the top of a Lucitrap captured 30-300 times more L. sericata then were captured inside an unaltered Lucitrap. Direct observation of metallic green calliphorids (92.1% L. sericata) alighting on Lucitraps indicated that most flies stayed for a short while (modal class 2-4 s) and only a few stayed longer, to an observed maximum of 28 s. Flies explored a mean of 1.5 entry holes (range 0-7) during a visit but only 6% entered the trap. Size of L. sericata was not a physical barrier to Lucitrap entry, because many larger species were captured. However, L. sericata captured inside Lucitraps were significantly smaller than those captured on sticky traps, demonstrating that size was of behavioural importance. The data demonstrate that the Lucitrap is not effective as a trap for L. sericata in Hungary, due mainly to a failure of flies to enter the trap in large numbers. In Australia and South Africa, L. sericata is commonly caught in Lucitraps baited with Lucilure, although L. cuprina is more numerous. Our study highlights the potential for diversity of fly behaviour between different geographical populations of the same species. Such diversity can have a significant effect on the functioning of systems for fly sampling and control, when these systems depend for their success on certain behavioural responses of the target species. 相似文献