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排序方式: 共有159条查询结果,搜索用时 15 毫秒
151.
Dennis V Pedersen Gregers R Andersen Dennis V Pedersen Lubka Roumenina Rasmus K Jensen Trine AF Gadeberg Chiara Marinozzi Capucine Picard Tania Rybkine Steffen Thiel Uffe BS Sørensen Cordula Stover Veronique Fremeaux-Bacchi Gregers R Andersen 《The EMBO journal》2017,36(8):1084-1099
Properdin (FP) is an essential positive regulator of the complement alternative pathway (AP) providing stabilization of the C3 and C5 convertases, but its oligomeric nature challenges structural analysis. We describe here a novel FP deficiency (E244K) caused by a single point mutation which results in a very low level of AP activity. Recombinant FP E244K is monomeric, fails to support bacteriolysis, and binds weakly to C3 products. We compare this to a monomeric unit excised from oligomeric FP, which is also dysfunctional in bacteriolysis but binds the AP proconvertase, C3 convertase, C3 products and partially stabilizes the convertase. The crystal structure of such a FP-convertase complex suggests that the major contact between FP and the AP convertase is mediated by a single FP thrombospondin repeat and a small region in C3b. Small angle X-ray scattering indicates that FP E244K is trapped in a compact conformation preventing its oligomerization. Our studies demonstrate an essential role of FP oligomerization in vivo while our monomers enable detailed structural insight paving the way for novel modulators of complement. 相似文献
152.
W H Stork J A Van Boxsel A F De Goeij AF+DEGOEIJ P L De Haseth PL+DEHASETH M Mandel 《Biophysical chemistry》1974,2(2):127-136
Binding of auramine O to poly-(methacrylic acid) (PMA) has been established over a large range of C0p/C0d values using spectroscopic methods (UV absorption and visible fluorescence emission spectra), equilibrium and sedimentation dialysis, potentiometric and viscosimetric titrations. All the results show qualitative agreement with those obtained previously with the system crystal violet-PMA although the binding seems to be less strong for auramine O than for crystal violet. From dialysis experiments binding isotherms were obtained at three different degrees of neutralization α'; at α' = 0.10 the results could be fitted to a Langmuir isotherm but at α' equal to 0.40 and 0.65 deviations with respect to such an isotherm occur. The results of potentiometric and viscosimetric titrations confirm that the conformational transition which the dye-free PMA exhibits upon ionization is affected by the dye binding. The region in which the conformational transion occurs is broadened and is less sharply defined in the presence of auramine O. 相似文献
153.
B Aton A G Doukas R H Callender B Becher T G Ebrey 《Biochimica et biophysica acta》1979,576(2):424-428
The resonance Raman spectrum of the dark-adapted form of the purple membrane protein (bacteriorhodopsin) has been obtained and is compared to the light-adapted pigment and model chromophore spectra. As in the light-adapted form, the chromophore-protein linkage is found to be a protonated Schiff base. Electron delocalization appears to play the dominant role in color regulation. The dark-adapted spectrum indicates a conformation closer to 13-cis than the light-adapted spectrum. 相似文献
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159.
Long-term history of chemoautotrophic clam-dominated faunas of petroleum seeps in the Northwestern Gulf of Mexico 总被引:2,自引:0,他引:2
Summary Chemoautotrophic clam-dominated assemblages are commonly associated with petroleum seepage on the continental slope of the
Gulf of Mexico. We examine the persistence and resilence of these communities by evaluating downcore trends in abundance,
biomass, and trophodynamics in communities from four separate petroleum seep sites on the Louisiana continental slope. Some
petroleum seep sites retained optimal habitat for some species continuously over geologically-relevant periods of time. More
commonly, however, habitat optimality varied substantially over time scales of hundreds of years. Thus, one important characteristic
of these sites was the degree of persistence of the chemoautotrophic biota. A fauna typically was persistent over a time span
of a few hundred years, but was typically not persistent over a longer time span. The mechanisms producing local extinction
remain unclear, however temporal variations in juvenile survivorship seem to be substantially larger than temporal variations
in larval settlement, to the extent that the heavily taphonomically-biased record of juvenile individuals permits such a conclusion.
When local extinctions occurred in the chemoautotrophic biota, the biota was replaced by a normal slope biota or a mixture
of a normal slope biota and the juveniles of chemoautotrophic species that failed to survive to adulthood. Thus, the only
faunal transitions were between specific chemoautotrophic faunas and the non-chemoautotrophic fauna. Not one distinctive faunal
transition between two chemoautotrophic faunas was observed. Accordingly, each discrete chemoautotrophic fauna was resilient
over long time scales; time scales of geological importance. 相似文献