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901.
902.
903.
Radda Rusinova E. Ashley Hobart Roger E. Koeppe II Olaf S. Andersen 《The Journal of general physiology》2013,141(6):673-690
Phosphatidylinositol-4,5-bisphosphate (PIP2), which constitutes ∼1% of the plasma membrane phospholipid, plays a key role in membrane-delimited signaling. PIP2 regulates structurally and functionally diverse membrane proteins, including voltage- and ligand-gated ion channels, inwardly rectifying ion channels, transporters, and receptors. In some cases, the regulation is known to involve specific lipid–protein interactions, but the mechanisms by which PIP2 regulates many of its various targets remain to be fully elucidated. Because many PIP2 targets are membrane-spanning proteins, we explored whether the phosphoinositides might alter bilayer physical properties such as curvature and elasticity, which would alter the equilibrium between membrane protein conformational states—and thereby protein function. Taking advantage of the gramicidin A (gA) channels’ sensitivity to changes in lipid bilayer properties, we used gA-based fluorescence quenching and single-channel assays to examine the effects of long-chain PIP2s (brain PIP2, which is predominantly 1-stearyl-2-arachidonyl-PIP2, and dioleoyl-PIP2) on bilayer properties. When premixed with dioleoyl-phosphocholine at 2 mol %, both long-chain PIP2s produced similar changes in gA channel function (bilayer properties); when applied through the aqueous solution, however, brain PIP2 was a more potent modifier than dioleoyl-PIP2. Given the widespread use of short-chain dioctanoyl-phosphoinositides, we also examined the effects of diC8-phosphoinositol (PI), PI(4,5)P2, PI(3,5)P2, PI(3,4)P2, and PI(3,4,5)P3. The diC8 phosphoinositides, except for PI(3,5)P2, altered bilayer properties with potencies that decreased with increasing head group charge. Nonphosphoinositide diC8 phospholipids generally were more potent bilayer modifiers than the polyphosphoinositides. These results show that physiological increases or decreases in plasma membrane PIP2 levels, as a result of activation of PI kinases or phosphatases, are likely to alter lipid bilayer properties, in addition to any other effects they may have. The results further show that exogenous PIP2, as well as structural analogues that differ in acyl chain length or phosphorylation state, alters lipid bilayer properties at the concentrations used in many cell physiological experiments. 相似文献
904.
905.
Kh. S. Vishniakova I. I. Kireev A. Ya. Dunina-Barkovskaya 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2011,5(4):355-363
Cell culture density is shown to alter the parameters characterizing phagocytic activity of cells in vitro. Phagocytosis index
(PI, mean number of beads per cell in the bead-containing population) and phagocytosis percent (PP, percentage of bead-containing
cells in cell population under study) for IC-21 macrophages incubated in the presence of non-opsonized 2-μm fluorescent latex
beads were determined using fluorescent microscopy and ImageJ software specially adapted for the purpose. Under control conditions
(DMEM without serum), increase in cell culture density was accompanied with a decrease of both parameters of the phagocytic
activity. At a mean density of 4 cells/105 μm2 (9 cells per a viewfield) PI was 7.1 ± 0.2 beads/cell and at 20 cells/105 μm2 (40 cells per a viewfield) PI dropped to 4.6 ± 0.1 beads/cell. PP was less sensitive, varied in the range of 95–100% but
also decreased as the cell density grew. At any density, PI was 1.5–2 times higher than the expected value (number of beads
per μm2 × cell contour area); apparently this divergence can be accounted for by cell locomotion and capture of a larger number of
beads than could drop onto a motionless cell with a constant contour area. Increase in cell density was also accompanied by
a decrease of the cell contour area (S
c), which amounted to 750 ± 16 μm2 at a density of 4 cells/105 μm2 and 346 ± 4 μm2 at a density of 20 cells/105 μm2. As the bead concentration was the same in all experiments, density-dependent decrease in PI and PP may be related with the
observed decrease in cell contour area. Yet, the bead number per cell area unit (PI/S
c) was bigger at higher density and PI/S
c was higher in cells with smaller S
c. Thus, individual (specific) activity of the cells did not lessen with an increase of the cell culture density in the range
studied (4–20 cells/105 μm2). Reduction of the cell contour area may reflect alteration in cell adhesion to the substrate as well as competitive relations
between adhesion and phagocytic processes. The data obtained imply that cell culture density has to be controlled as a factor
notably altering the phagocytic activity parameters. The effects of serum, methyl-β-cyclodextrin, and carbenoxolon reported
earlier [Golovkina et al. 2009. Biol membrany. 26 (5), 379–386] are re-evaluated and confirmed here. 相似文献
906.
The lacdiNAc sequence GalNAcß1 相似文献
907.
DAVID B. TAYLOR ALLEN L. SZALANSKI RICHARD D. PETERSON II 《Medical and veterinary entomology》1996,10(1):63-70
Abstract. Restriction fragment length polymorphisms in polymerase chain reaction amplified fragments (PCR-RFLP) of mitochondrial DNA were used to differentiate species of New World screwworms (Diptera: Calliphoridae). Twenty-seven restriction enzymes were screened on five regions of mtDNA. Eleven restriction fragment length patterns differentiated New World screwworm, Cochliomyia hominivorax (Coquerel), from secondary screwworm, Cochliomyia macellaria (R). Five restriction fragment length patterns were polymorphic in C. hominivorax while all fragment patterns were fixed in C. macellaria. Diagnostic restriction fragment length patterns were used for species diagnosis, whereas intraspecific variable patterns were used to characterize field samples and laboratory strains. The PCR-RFLP technique is flexible with regard to developmental stage of the sample and method of preservation. We were able to characterize specimens of all life stages from egg to adult including larvae preserved in alcohol and pinned adults. PCR-RFLP is rapid and inexpensive, enabling specimens to be characterized within 24 h for less than 2.50. 相似文献
908.
David W. Deerfield II Amanda M. Holland-Minkley Joe Geigel Hugh B. Nicholas Jr. 《Journal of Protein Chemistry》1997,16(5):441-447
We have studied the classification of the environment of residues within protein structures. Eisenberg's original idea created environmental categories to discriminate between similar residues [Bowie et al., Science (1991), 253, 164–170]. These environments grouped residues based upon their buried surface area, polarity of the surrounding environment, and secondary structure element in which the residue is found. However, Eisenberg's original categories led to incomplete discrimination between residues that only partially substitute for each other. We have expanded on Eisenberg's original idea of environmental categories, by both considering additional contacts in the calculation of the solvent-accessible molecular surface area and by subdividing the environmental plot into regions based upon its theoretical features. Our alternative surface area calculations were used in conjunction with the polarity of the environment of the residue to define a new set of environmental categories. These new categories were able to discriminate between residues such as threonine, valine, and aspartic acid while reflecting the propensity of these residues to substitute for each other. 相似文献