Novel type of red-shifted chlorophyll a antenna complex from Chromera velia: II. Biochemistry and spectroscopy

A novel chlorophyll a containing pigment–protein complex expressed by cells of Chromera velia adapted to growth under red/far-red illumination [1]. Purification of the complex was achieved by means of anion-exchange chromatography and gel-filtration. The antenna is shown to be an aggregate of ~ 20 kDa proteins of the light–harvesting complex (LHC) family, unstable in the isolated form. The complex possesses an absorption maximum at 705 nm at room temperature in addition to the main chlorophyll a maximum at 677 nm producing the major emission band at 714 nm at room temperature. The far-red absorption is shown to be the property of the isolated aggregate in the intact form and lost upon dissociation. The purified complex was further characterized by circular dichroism spectroscopy and fluorescence spectroscopy. This work thus identified the third different class of antenna complex in C. velia after the recently described FCP-like and LHCr-like antennas. Possible candidates for red antennas are identified in other taxonomic groups, such as eustigmatophytes and the relevance of the present results to other known examples of red-shifted antenna from other organisms is discussed. This work appears to be the first successful isolation of a chlorophyll a-based far-red antenna complex absorbing above 700 nm unrelated to LHCI.     

Ca2+ and calmodulin antagonists inhibit the proton gradients associated with non-cyclic and cyclic photophosphorylation in spinach chloroplasts

The synthesis of benzylpenicillin (BP) after mixing phenyl-acetyl-glycine(PAG), 6-aminopenicillanic acid (6-APA) and free or immobilized penicillin amidase (E.C.3.5.1.11.) was studied as a function of pH and ionic strength. Before the final equilibrium was reached a kinetically controlled synthesis of BP was observed. Then a transient maximum concentration in BP much larger than the final equilibrium content was synthesized in the acyl-transfer process. The factors influencing this maximum have been analyzed. Increasing ionic strength markedly decreased the maximum in BP and the rate of deacylation of phenyl-acetyl-penicillin amidase by 6-APA. The change was largest when the enzyme was immobilized in a positively charged support, where at low ionic strength the concentration of 6-APA around the enzyme is larger than the bulk concentration due to the partitioning of charged solutes.     

病毒干扰MHCⅠ类抗原呈递策略的研究进展

细胞表面MHCⅠ类分子在CTL的产生和作为CTL受体的配体清除病毒感染细胞中发挥着重要作用。因此,许多病毒在其生活周期的不同阶段干扰MHCⅠ类抗原呈递并不足为奇。深入理解病毒利用的干扰策略不仅有助于揭示病毒的致病机理,而且有助于制定新的对策避免病毒逃逸,这些研究最终可能建立有效控制病毒感染的免疫疗法。因此,本文将就病毒干扰MHCⅠ类抗原呈递策略的研究进展做一综述。     

Characteristics of the Photosystem II reaction centre. II. Electron donors

The properties of Photosystem II electron donation were investigated by EPR spectrometry at cryogenic temperatures. Using preparations from mutants which lacked Photosystem I, the main electron donor through the Photosystem II reaction centre to the quinone-iron acceptor was shown to be the component termed Signal II. A radical of 10 G line width observed as an electron donor at cryogenic temperatures under some conditions probably arises through modification of the normal pathway of electron donation. High-potential cytochrome b-559 was not observed on the main pathway of electron donation. Two types of PS II centres with identical EPR components but different electron-transport kinetics were identified, together with anomalies between preparations in the amount of Signal II compared to the quinone-iron acceptor. Results of experiments using cells from mutants of Scenedesmus obliquus confirm the involvement of the Signal II component, manganese and high-potential cytochrome b-559 in the physiological process leading to oxygen evolution.     

Reconstitution of the Turkey erythrocyte adenylate cyclase sensitivity to l-epinephrine upon re-insertion of the Lubrol solubilized components into phospholipid vesicles

Turkey erythrocyte adenylate cyclase was activated by GppNHp and l-epinephrine to its stable, highly active form. In this form the enzyme could be solubilized by Lubrol-PX and subsequently re-inserted into phospholipid vesicles concomitantly with the removal of up to 99.3% of the Lubrol. The ability of GTP and l-epinephrine to reverse the GppNHp/epinephrine activated state was taken as a measure for the reappearance of hormone sensitivity in the reconstituted vesicles. An incomplete but significant reappearance of hormone sensitivity in the reconstituted adenylate cyclase was achieved. This hormone sensitivity was found to be stereospecific for (?)epinephrine. The ¹²⁵I-cyanopindolol binding properties of the reconstituted β-receptor depend on the nature of the detergent and the phospholipids used in the reconstitution.     

5型肺炎链球菌荚膜多糖结合疫苗的不同糖蛋白比与免疫原性的关系

实验中比较了以不同糖蛋白比结合的5型肺炎链球菌荚膜多糖结合疫苗的免疫原性。以氨还原法制备的不同糖蛋白比的5型多糖结合疫苗分别经腹腔注射NIH小鼠,共免疫3次,间隔2周。末次免疫2周后采血分离血清,以间接ELISA测定血清抗体,t检验统计分析数据。结果显示,生理盐水组(R组)无免疫原性;5型荚膜多糖组(H组)免疫原性低,无免疫加强效应;结合疫苗M组、N组第1、2针有免疫加强效应,第2、3针无免疫加强效应,而F组和Q组的两针次间均有明显的免疫加强效应。说明5型肺炎链球菌荚膜多糖结合疫苗的糖与蛋白比较高时能获得较好的免疫原性。     

Structure of antimicrobial peptides and lipid membranes probed by interface-sensitive X-ray scattering

The conformation and correlations of amphiphilic and antimicrobial peptides and the associated changes of lipid bilayers can be studied in oriented lipid membranes deposited on solid substrates. Here we review recent work on these systems, as studied by modern interface-sensitive X-ray and neutron scattering methods. Density profile, short range order of acyl chains and molecular conformations of peptides and lipids are probed in the fluid state of the bilayer. With an emphasis on technical aspects, we review recent work illustrating the potential of the methods and discuss its potential in the field.     

Proton-induced grana formation in chloroplasts. Distribution of chlorophyll-protein complexes and Photosystem II photochemistry

Lowering the pH of the incubation medium to pH 5.4 leads to grana formation morphologically similar to that induced by metal cations. The same phenomenon is observed in EDTA-washed chloroplasts, indicating that it is not due in part to electrostatic ‘masking’ by residual cations associated with the membranes. Digitonin fractionation studies have indicated that the distribution of the major chlorophyll-protein complexes between granal and stromal membrane regions is similar at pH 5.4 in the absence of Mg²⁺, and at pH 7.4 in the presence of Mg²⁺. Chlorophyll fluorescence induction studies have indicated that the primary photochemistry of Photosystem II (PS II) is stimulated by lowering the pH to 5.4, just as it is upon metal cation addition at higher pH values. The failure to observe such an increase at pH 5.4 by measuring electron transport to ferricyanide is attributed to a combination of an inhibition by this pH of electron transport at a site after Q reduction and an increase in the number of PS II centres detached from the plastoquinone pool. We conclude that the stacked configuration of chloroplast membranes leads to increased PS II primary photochemistry, which is most simply explained in terms of a redistribution of excitation energy towards PS II.     

The Role of the Lipid Bilayer in Tau Aggregation

Tau is a microtubule associated protein whose aggregation is implicated in a number of neurodegenerative diseases. We investigate the mechanism by which anionic lipid vesicles induce aggregation of tau in vitro using K18, a fragment of tau corresponding to the four repeats of the microtubule binding domain. Our results show that aggregation occurs when the amount of K18 bound to the lipid bilayer exceeds a critical surface density. The ratio of protein/lipid at the critical aggregation concentration is pH-dependent, as is the binding affinity. At low pH, where the protein binds with high affinity, the critical surface density is independent both of total lipid concentration as well as the fraction of anionic lipid present in the bilayer. Furthermore, the aggregates consist of both protein and vesicles and bind the β-sheet specific dye, Thioflavin T, in the manner characteristic of pathological aggregates. Our results suggest that the lipid bilayer facilitates protein-protein interactions both by screening charges on the protein and by increasing the local protein concentration, resulting in rapid aggregation. Because anionic lipids are abundant in cellular membranes, these findings contribute to understanding tau-lipid bilayer interactions that may be relevant to disease pathology.