首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
In vitro studies of the carotenoid peridinin, which is the primary pigment from the peridinin chlorophyll-a protein (PCP) light harvesting complex, showed a strong dependence on the lifetime of the peridinin lowest singlet excited state on solvent polarity. This dependence was attributed to the presence of an intramolecular charge transfer (ICT) state in the peridinin excited state manifold. The ICT state was also suggested to be a crucial factor in efficient peridinin to Chl-a energy transfer in the PCP complex. Here we extend our studies of peridinin dynamics to reconstituted PCP complexes, in which Chl-a was replaced by different chlorophyll species (Chl-b, acetyl Chl-a, Chl-d and BChl-a). Reconstitution of PCP with different Chl species maintains the energy transfer pathways within the complex, but the efficiency depends on the chlorophyll species. In the native PCP complex, the peridinin S1/ICT state has a lifetime of 2.7 ps, whereas in reconstituted PCP complexes it is 5.9 ps (Chl-b) 2.9 ps (Chl-a), 2.2 ps (acetyl Chl-a), 1.9 ps (Chl-d), and 0.45 ps (BChl-a). Calculation of energy transfer rates using the Förster equation explains the differences in energy transfer efficiency in terms of changing spectral overlap between the peridinin emission and the absorption spectrum of the acceptor. It is proposed that the lowest excited state of peridinin is a strongly coupled S1/ICT state, which is the energy donor for the major energy transfer channel. The significant ICT character of the S1/ICT state in PCP enhances the transition dipole moment of the S1/ICT state, facilitating energy transfer to chlorophyll via the Förster mechanism. In addition to energy transfer via the S1/ICT, there is also energy transfer via the S2 and hot S1/ICT states to chlorophyll in all reconstituted PCP complexes.  相似文献   

2.
Acaryochloris marina is an oxygen-evolving organism that utilizes chlorophyll-d for light induced photochemistry. In photosystem I particles from Acaryochloris marina, the primary electron donor is called P740, and it is thought that P740 consist of two chlorophyll-d molecules. (P740+-P740) FTIR difference spectra have been produced, and vibrational features that are specific to chlorophyll-d (and not chlorophyll-a) were observed, supporting the idea that P740 consists chlorophyll-d molecules. Although bands in the (P740+-P740) FTIR difference spectra were assigned specifically to chlorophyll-d, how these bands shifted, and how their intensities changed, upon cation formation was never considered. Without this information it is difficult to draw unambiguous conclusions from the FTIR difference spectra. To gain a more detailed understanding of cation induced shifting of bands associated with vibrational modes of P740 we have used density functional theory to calculate the vibrational properties of a chlorophyll-d model in the neutral, cation and anion states. These calculations are shown to be of considerable use in interpreting bands in (P740+-P740) FTIR difference spectra. Our calculations predict that the 31 formyl C–H mode of chlorophyll-d upshifts/downshifts upon cation/anion formation, respectively. The mode intensity also decreases/increases upon cation/anion formation, respectively. The cation induced bandshift of the 31 formyl C–H mode of chlorophyll-d is also strongly dependant on the dielectric environment of the chlorophyll-d molecules. With this new knowledge we reassess the interpretation of bands that were assigned to 31 formyl C–H modes of chlorophyll-d in (P740+-P740) FTIR difference spectra. Considering our calculations in combination with (P740+-P740) FTIR DS we find that the most likely conclusions are that P740 is a dimeric Chl-d species, in an environment of low effective dielectric constant (∼2–8). In the P740+ state, charge is asymmetrically distributed over the two Chl-d pigments in a roughly 60:40 ratio. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

3.
Bacteriochlorophyll(BChl)-f which has not yet been found in natural phototrophs was prepared by chemically modifying chlorophyll-b. The retention time of reverse-phase high-performance liquid chromatography of the synthetic monomeric BChl-f as well as its visible absorption and fluorescence emission spectra in a solution were identified and compared with other naturally occurring chlorophyll pigments obtained from the main light-harvesting antenna systems of green sulfur bacteria, BChls-c/d/e. Based on the above data, BChl-f was below the level of detection in three strains of green photosynthetic bacteria producing BChl-e.  相似文献   

4.
The mutant lacking the enzyme BciA (renamed CT1063), which catalyzed reduction of the 8-vinyl group of a porphyrinoid-type 3,8-divinyl-(proto)chlorophyllide-a [DV-(P)Chlide-a] in the green sulfur bacterium Chlorobaculum (Cba.) tepidum, was reconstructed on the basis of the previous study reported by Chew and Bryant [J. Biol. Chem. 2007, 282, 2967–2975]. Cba. tepidum biosynthesizes the following three different types of chlorophylls (Chls) through their common precursory DV-(P)Chlide-a as its photosynthetically active pigments: bacteriochlorophyll(BChl)-c and Chl-a with the partially reduced 17,18-trans-dihydroporphyrin and BChl-a with the further reduced 7,8-trans-17,18-trans-tetrahydroporphyrin. The structures of Chls thus produced were characterized in detail by various spectroscopic techniques. In the mutant, both BChl-c and Chl-a possessing the alkyl group at the 8-position were exclusively replaced by their 8-vinylated derivatives, whereas BChl-a possessed the original 8-ethyl group. The present observations were inconsistent with the previous report. However, it was apparently confirmed that the enzyme BciA was responsible for the reduction of DV-(P)Chlide-a to produce BChl-c and Chl-a. Noteworthily, exclusive accumulation of the reduced (8-ethylated) form of BChl-a, not its 8-vinylated derivative, in the mutant indicates the presence of another enzyme catalyzing the 8-vinyl reduction as yet unidentified or any other reduction mechanism using a known enzyme to yield BChl-a.  相似文献   

5.
The polarization anisotropy of fluorescence spectra from single chlorosomes isolated from a green sulfur bacterium, Chlorobium (Cb.) tepidum, was observed at 13 K. As the polarizer was rotated, the intensities of the fluorescence bands of both bacteriochlorophyll (BChl)-c self-aggregates and BChl-a in baseplate proteins showed clear oscillations. From the oscillation, the values of the degree of polarization (DP) and the phase shift (PS) between the BChl-c and BChl-a bands were determined for each single chlorosome. The DP versus PS plot for Cb. tepidum chlorosomes showed linear correlations between the PS and the DP values for both BChl-c and BChl-a fluorescence bands. This tendency could be explained from a simulation assuming a random orientation of chlorosomes and a triaxial orientation distribution of emitting transition dipoles within a single chlorosome. The intensity ratios among the X-/Y-/Z-principal transition dipoles were estimated to be 0.3/0.5/1 and 1/0.6/0.1 for the BChl-c and BChl-a fluorescence bands, respectively. Here, the X-, Y-, and Z-axes are perpendicular, parallel to the cytoplasmic membrane, and parallel to the chlorosome long axis, respectively. A theoretical calculation based on the exciton theory was conducted to reproduce the observed triaxial orientation distribution of emitting transition dipoles. The simulation revealed that a deformation introduced to the circular cross section of the rod-shaped BChl-c self-aggregates could qualitatively reproduce results of this study.  相似文献   

6.
Intramolecular correlations among the 18O-labels of metabolic oligophosphates, mapped by J-decoupled 31P NMR 2D chemical shift correlation spectroscopy, impart stringent constraints to the 18O-isotope distributions over the whole oligophosphate moiety. The multiple deduced correlations of isotopic labels enable determination of site-specific fractional isotope enrichments and unravel the isotopologue statistics. This approach ensures accurate determination of 18O-labeling rates of phosphometabolites, critical in biochemical energy conversion and metabolic flux transmission. The biological usefulness of the J-decoupled 31P NMR 2D chemical shift correlation maps was validated on adenosine tri-phosphate fractionally 18O labeled in perfused mammalian hearts.  相似文献   

7.
The cyanobacterium Acaryochloris marina was cultured in the presence of either H218O or 18O2, and the newly synthesized chlorophylls (Chl a and Chl d) were isolated using high performance liquid chromatography and analyzed by mass spectroscopy. In the presence of H218O, newly synthesized Chl a and d, both incorporated up to four isotopic 18O atoms. Time course H218O labeling experiments showed incorporation of isotopic 18O atoms originating from H218O into Chl a, with over 90% of Chl a 18O-labeled at 48 h. The incorporation of isotopic 18O atoms into Chl d upon incubation in H218O was slower compared with Chl a with ∼50% 18O-labeled Chl d at 115 h. The rapid turnover of newly synthesized Chl a suggested that Chl a is the direct biosynthetic precursor of Chl d. In the presence of 18O2 gas, one isotopic 18O atom was incorporated into Chl a with approximately the same kinetic incorporation rate observed in the H218O labeling experiment, reaching over 90% labeling intensity at 48 h. The incorporation of two isotopic 18O atoms derived from molecular oxygen (18O2) was observed in the extracted Chl d, and the percentage of double isotopic 18O-labeled Chl d increased in parallel with the decrease of non-isotopic-labeled Chl d. This clearly indicated that the oxygen atom in the C31-formyl group of Chl d is derived from dioxygen via an oxygenase-type reaction mechanism.  相似文献   

8.
Heavy water (H218O) has been used to label DNA of soil microorganisms in stable isotope probing experiments, yet no measurements have been reported for the 18O content of DNA from soil incubated with heavy water. Here we present the first measurements of atom% 18O for DNA extracted from soil incubated with the addition of H218O. Four experiments were conducted to test how the atom% 18O of DNA, extracted from Ponderosa Pine forest soil incubated with heavy water, was affected by the following variables: (1) time, (2) nutrients, (3) soil moisture, and (4) atom% 18O of added H2O. In the time series experiment, the atom% 18O of DNA increased linearly (R 2 = 0.994, p < 0.01) over the first 72 h of incubation. In the nutrient addition experiment, there was a positive correlation (R 2 = 0.991, p = 0.006) between the log10 of the amount of tryptic soy broth, a complex nutrient broth, added to soil and the log10 of the atom% 18O of DNA. For the experiment where soil moisture was manipulated, the atom% 18O of DNA increased with higher soil moisture until soil moisture reached 30%, above which 18O enrichment of DNA declined as soils became more saturated. When the atom% 18O for H2O added was varied, there was a positive linear relationship between the atom% 18O of the added water and the atom% 18O of the DNA. Results indicate that quantification of 18O incorporated into DNA from H218O has potential to be used as a proxy for microbial growth in soil.  相似文献   

9.

Introduction

Oxygen from carbon dioxide, water or molecular oxygen, depending on the responsible enzyme, can lead to a large variety of metabolites through chemical modification.

Objectives

Pathway-specific labeling using isotopic molecular oxygen (18O2) makes it possible to determine the origin of oxygen atoms in metabolites and the presence of biosynthetic enzymes (e.g., oxygenases). In this study, we established the basis of 18O2-metabolome analysis.

Methods

18O2 labeled whole Medicago truncatula seedlings were prepared using 18O2-air and an economical sealed-glass bottle system. Metabolites were analyzed using high-accuracy and high-resolution mass spectrometry. Identification of the metabolite was confirmed by NMR following UHPLC–solid-phase extraction (SPE).

Results

A total of 511 peaks labeled by 18O2 from shoot and 343 peaks from root were annotated by untargeted metabolome analysis. Additionally, we identified a new flavonoid, apigenin 4′-O-[2′-O-coumaroyl-glucuronopyranosyl-(1–2)-O-glucuronopyranoside], that was labeled by 18O2. To the best of our knowledge, this is the first report of apigenin 4′-glucuronide in M. truncatula. Using MSn analysis, we estimated that 18O atoms were specifically incorporated in apigenin, the coumaroyl group, and glucuronic acid. For apigenin, an 18O atom was incorporated in the 4′-hydroxy group. Thus, non-specific incorporation of an 18O atom by recycling during one month of labeling is unlikely compared with the more specific oxygenase-catalyzing reaction.

Conclusion

Our finding indicated that 18O2 labeling was effective not only for the mining of unknown metabolites which were biosynthesized by oxygenase-related pathway but also for the identification of metabolites whose oxygen atoms were derived from oxygenase activity.
  相似文献   

10.
Described here is a set of three-dimensional (3D) NMR experiments that rely on CACA-TOCSY magnetization transfer via the weak 3 \textJ\textCa\textCa ^{ 3} {\text{J}}_{{{\text{C}}\alpha {\text{C}}\alpha }} coupling. These pulse sequences, which resemble recently described 13C detected CACA-TOCSY (Takeuchi et al. 2010) experiments, are recorded in 1H2O, and use 1H excitation and detection. These experiments require alternate 13C-12C labeling together with perdeuteration, which allows utilizing the small 3 \textJ\textCa\textCa ^{ 3} {\text{J}}_{{{\text{C}}\alpha {\text{C}}\alpha }} scalar coupling that is otherwise masked by the stronger 1JCC couplings in uniformly 13C labeled samples. These new experiments provide a unique assignment ladder-mark that yields bidirectional supra-sequential information and can readily straddle proline residues. Unlike the conventional HNCA experiment, which contains only sequential information to the 1 3 \textCa ^{ 1 3} {\text{C}}^{\alpha } of the preceding residue, the 3D hnCA-TOCSY-caNH experiment can yield sequential correlations to alpha carbons in positions i1, i + 1 and i2. Furthermore, the 3D hNca-TOCSY-caNH and Hnca-TOCSY-caNH experiments, which share the same magnetization pathway but use a different chemical shift encoding, directly couple the 15N-1H spin pair of residue i to adjacent amide protons and nitrogens at positions i2, i1, i + 1 and i + 2, respectively. These new experimental features make protein backbone assignments more robust by reducing the degeneracy problem associated with the conventional 3D NMR experiments.  相似文献   

11.
Five closed saline lakes near Humboldt, Saskatchewan, were found to be meromictic. Two of these lakes (Waldsea, Deadmoose) were first discovered to be meromictic in the early 1970s and three (Arthur, Marie, Sayer) in 1985. The origin of their meromixis is ectogenic. One of the lakes, Waldsea, had surface salinities far higher in 1960–1961 than those of 1970 or later and as high as that of the monimolimnion occasionally was from 1970 to the present. During the late 1960s to 1980 the lake level of Waldsea rose four metres as a result of higher than normal snowpacks and subsequent high snowmelt runoff. Endogenic processes of freezing out of salts from the upper metre during ice formation and precipitation of sodium sulphate during autumn cooling also promote meromixis. The lakes which are located in depressions in a relatively flat topography are very exposed to periodic high velocity westerly winds. Although Deadmoose and Waldsea lakes are relatively deep, Arthur, Marie and Sayer lakes have maximum depths of only three to five metres. Meromixis has persisted until the present in three lakes but Marie and Arthur lakes became holomictic during the autumn of 1988, a severe drought year. Bacterial plates were prominent in Waldsea, Deadmoose and Sayer lakes. BChl-a and BChl-d were present in 1988 with maxima of 2652 mg · m−3 BChl-a and 4290 mg · m−3 BChl-d in Sayer Lake. BChl-a virtually disappeared in subsequent years.  相似文献   

12.
The peridinin-chlorophyll a-protein (PCP) from dinoflagellates is a soluble light harvesting antenna which gathers incoming photons mainly by the carotenoid peridinin. In PCPs reconstituted with different chlorophylls, the peridinin to chlorophyll energy transfer rates are well predicted by a Förster-like theory, but only if the pigment arrangements are identical in all PCPs. We have determined the X-ray structures of PCPs reconstituted with Chlorophyll-b (Chl-b), Chlorophyll-d (Chl-d) and Bacteriochlorophyll-a (BChl-a) to resolutions ?2 Å. In all three cases the pigment arrangements are essentially the same as in native PCP. Hydrogen bonding is not responsible for preferential incorporation of “non-native” chlorophylls over Chl-a.  相似文献   

13.
Selective isotopic labeling provides an unparalleled window within which to study the structure and dynamics of RNAs by high resolution NMR spectroscopy. Unlike commonly used carbon sources, the asymmetry of 13C-labeled pyruvate provides selective labeling in both the ribose and base moieties of nucleotides using E. coli variants, that until now were not feasible. Here we show that an E. coli mutant strain that lacks succinate and malate dehydrogenases (DL323) and grown on [3-13C]-pyruvate affords ribonucleotides with site specific labeling at C5′ (~95%) and C1′ (~42%) and minimal enrichment elsewhere in the ribose ring. Enrichment is also achieved at purine C2 and C8 (~95%) and pyrimidine C5 (~100%) positions with minimal labeling at pyrimidine C6 and purine C5 positions. These labeling patterns contrast with those obtained with DL323 E. coli grown on [1, 3-13C]-glycerol for which the ribose ring is labeled in all but the C4′ carbon position, leading to multiplet splitting of the C1′, C2′ and C3′ carbon atoms. The usefulness of these labeling patterns is demonstrated with a 27-nt RNA fragment derived from the 30S ribosomal subunit. Removal of the strong magnetic coupling within the ribose and base leads to increased sensitivity, substantial simplification of NMR spectra, and more precise and accurate dynamic parameters derived from NMR relaxation measurements. Thus these new labels offer valuable probes for characterizing the structure and dynamics of RNA that were previously limited by the constraint of uniformly labeled nucleotides.  相似文献   

14.
Rhizoctonia solani AG-3 is a soilborne plant pathogen that forms resting vegetative structures called sclerotia. These compact structures are crucial to the pathogen’s survival and pathogenesis. The metabolic changes occurring during sclerotia development were monitored using proton nuclear magnetic resonance (1H NMR) spectroscopy and gas chromatography–mass spectrometry (GC-MS). The validation, discrimination, and the establishment of correlative relationships between metabolite signals were performed by principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA). The results of the analyses suggested that out of the 116 compounds that were simultaneously analyzed and compared using GC-MS, α-α-trehalose, d-glucose, 9-(Z)-octadecenoic and 9,12-octadecadienoic acids, xylitol, and glucitol were key metabolites that were highly dependent on the developmental stage of the sclerotia contributing to their discrimination and classification. Furthermore, the application of 1H NMR and GC-MS metabolic fingerprinting on the same biological sample provided complementary information illustrating the value of this integrated approach in the study of metabolic changes in fungal structures.  相似文献   

15.
NMR-spectroscopy enables unique experimental studies on protein dynamics at atomic resolution. In order to obtain a full atom view on protein dynamics, and to study specific local processes like ring-flips, proton-transfer, or tautomerization, one has to perform studies on amino-acid side chains. A key requirement for these studies is site-selective labeling with 13C and/or 1H, which is achieved in the most general way by using site-selectively 13C-enriched glucose (1- and 2-13C) as the carbon source in bacterial expression systems. Using this strategy, multiple sites in side chains, including aromatics, become site-selectively labeled and suitable for relaxation studies. Here we systematically investigate the use of site-selectively 13C-enriched erythrose (1-, 2-, 3- and 4-13C) as a suitable precursor for 13C labeled aromatic side chains. We quantify 13C incorporation in nearly all sites in all 20 amino acids and compare the results to glucose based labeling. In general the erythrose approach results in more selective labeling. While there is only a minor gain for phenylalanine and tyrosine side-chains, the 13C incorporation level for tryptophan is at least doubled. Additionally, the Phe ζ and Trp η2 positions become labeled. In the aliphatic side chains, labeling using erythrose yields isolated 13C labels for certain positions, like Ile β and His β, making these sites suitable for dynamics studies. Using erythrose instead of glucose as a source for site-selective 13C labeling enables unique or superior labeling for certain positions and is thereby expanding the toolbox for customized isotope labeling of amino-acid side-chains.  相似文献   

16.
Isotope labeling by residue type (LBRT) has long been an important tool for resonance assignments at the limit where other approaches, such as triple-resonance experiments or NOESY methods do not succeed in yielding complete assignments. While LBRT has become less important for small proteins it can be the method of last resort for completing assignments of the most challenging protein systems. Here we present an approach where LBRT is achieved by adding protonated 14N amino acids that are 13C labeled at the carbonyl position to a medium for uniform deuteration and 15N labeling. This has three important benefits over conventional 15N LBRT in a deuterated back ground: (1) selective TROSY-HNCO cross peaks can be observed with high sensitivity for amino-acid pairs connected by the labeling, and the amide proton of the residue following the 13C labeled amino acid is very sharp since its alpha position is deuterated, (2) the 13C label at the carbonyl position is less prone to scrambling than the 15N at the α-amino position, and (3) the peaks for the 1-13C labeled amino acids can be identified easily from the large intensity reduction in the 1H-15N TROSY-HSQC spectrum for some residues that do not significantly scramble nitrogens, such as alanine and tyrosine. This approach is cost effective and has been successfully applied to proteins larger than 40 kDa. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

17.
Agrocybe aegerita peroxidase/peroxygenase (AaP) is an extracellular fungal biocatalyst that selectively hydroxylates the aromatic ring of naphthalene. Under alkaline conditions, the reaction proceeds via the formation of an intermediary product with a molecular mass of 144 and a characteristic UV absorption spectrum (A max 210, 267, and 303 nm). The compound was semistable at pH 9 but spontaneously hydrolyzed under acidic conditions (pH <7) into 1-naphthol as major product and traces of 2-naphthol. Based on these findings and literature data, we propose naphthalene 1,2-oxide as the primary product of AaP-catalyzed oxygenation of naphthalene. Using 18O-labeled hydrogen peroxide, the origin of the oxygen atom transferred to naphthalene was proved to be the peroxide that acts both as oxidant (primary electron acceptor) and oxygen source.  相似文献   

18.
We recently constructed the mutant of the brown-colored green sulfur bacterium Chlorobaculum limnaeum lacking BciD which was responsible for formation of a formyl group at the 7-position in bacteriochlorophyll(BChl)-e biosynthesis. This mutant exclusively gave BChl-c, but not BChl-e, as the chlorosome pigments (Harada et al. in PLoS One 8(4):e60026, 2013). By the mutation, the homolog and epimer composition of the pigment was drastically altered. The methylation at the 82-position in the mutant cells proceeded to create BChl-c carrying large alkyl substituents at this position. Correspondingly, the content of BChls-c having the (S)-configuration at the chiral 31-position remarkably increased and accounted for 80.6 % of the total BChl-c. Based on the alteration of the pigment composition in the mutant cells, a new BChl-c bearing the bulkiest, triple 82-methylated neopentyl substituent at the 8-position ([N,E]BChl-c) was identified. The molecular structure of [N,E]BChl-c was fully determined by its NMR, mass, and circular dichroism spectra. The newly identified [N,E]BChl-c was epimerically pure at the chiral 31-position and its stereochemistry was determined to be an (S)-configuration by modified Mosher’s method. Further, the effects of the C82-methylation on the optical absorption properties of monomeric BChls-c were investigated. The Soret but not Qy absorption bands shifted to longer wavelengths by the extra methylation (at most 1.4 nm). The C82-methylation induced a slight but apparent effect on absorption properties of BChls-c in their monomeric states.  相似文献   

19.
The melanosome, an organelle specialized for melanin synthesis, is one of the lysosome-related organelles. Its lumen is reported to be acidified by vacuolar-type H+-ATPase (V-ATPase). Mammalian V-ATPase exhibits structural diversity in its subunit isoforms; with regard to membrane intrinsic subunit a, four isoforms (a1–a4) have been found to be localized to distinct subcellular compartments. In this study, we have shown that the a3 isoform is co-localized with a melanosome marker protein, Pmel17, in mouse melanocytes. Acidotropic probes (LysoSensor and DAMP) accumulate in non-pigmented Pmel17-positive melanosomes, and DAMP accumulation is sensitive to bafilomycin A1, a specific inhibitor of V-ATPase. However, none of the subunit a isoforms is associated with highly pigmented mature melanosomes, in which the acidotropic probes are also not accumulated. oc/oc mice, which have a null mutation at the a3 locus, show no obvious defects in melanogenesis. In the mutant melanocytes, the expression of the a2 isoform is modestly elevated, and a considerable fraction of this isoform is localized to premature melanosomes. These observations suggest that the V-ATPase keeps the lumen of premature melanosomes acidic, whereas melanosomal acidification is less significant in mature melanosomes. Ge-Hong Sun-Wada and Yoh Wada contributed equally to this study. This study was supported in part by Grants-in-Aid from the Ministry of Education, Culture, Sports, Science, and Technology of Japan and by the Hayashi and Noda Foundations.  相似文献   

20.
Circulating CD3+CD4+CD28- cells exhibit reduced apoptosis and were found to be more enriched in patients with ankylosing spondylitis than in age-matched healthy control individuals (7.40 ± 6.6% versus 1.03 ± 1.0%; P < 0.001). Levels of CD4+CD28- T cells correlate with disease status as measured using a modified metrology score, but they are independent of age and duration of ankylosing spondylitis. CD4+CD28- T cells produce IFN-γ and perforin, and thus they must be considered proinflammatory and cytotoxic. These T cells share phenotypic and functional properties of natural killer cells, strongly expressing CD57 but lacking the lymphocyte marker CD7. MHC class I recognizing and activating natural killer cell receptors on the surface of CD4+CD28- T cells may be involved in a HLA-B27 mediated co-stimulation of these proinflammatory and cytotoxic cells.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号