Selective disruption of energy flow from phycobilisomes to Photosystem I

Efficient production of ATP and NADPH by the light reactions of oxygen-evolving photosynthesis demands continuous adjustment of transfer of absorbed light energy from antenna complexes to Photosystem I (PS I) and II (PS II) reaction center complexes in response to changes in light quality. Treatment of intact cyanobacterial cells with N-ethylmaleimide appears to disrupt energy transfer from phycobilisomes to Photosystem I (PS I). Energy transfer from phycobilisomes to Photosystem II (PS II) is unperturbed. Spectroscopic analysis indicates that the individual complexes (phycobilisomes, PS II, PS I) remain functionally intact under these conditions. The results are consistent with the presence of connections between phycobiliproteins and both PS II and PS I, but they do not support the existence of direct contacts between the two photosystems.Abbreviations Chl chlorophyll - EPR electron paramagnetic resonance - NEM N-ethylmaleimide - PBS phycobilisome - PS photosystem     

Pore formation by the sea anemone cytolysin equinatoxin II in red blood cells and model lipid membranes

Summary The interaction ofActinia equina equinatoxin II (EqT-II) with human red blood cells (HRBC) and with model lipid membranes was studied. It was found that HRBC hemolysis by EqT-II is the result of a colloid-osmotic shock caused by the opening of toxin-induced ionic pores. In fact, hemolysis can be prevented by osmotic protectants of adequate size. The functional radius of the lesion was estimated to be about 1.1 nm. EqT-II increased also the permeability of calcein-loaded lipid vesicles comprised of different phospholipids. The rate of permeabilization rised when sphingomyelin was introduced into the vesicles, but it was also a function of the pH of the medium, optimum activity being between pH 8 and 9; at pH 10 the toxin became markedly less potent. From the dose-dependence of the permeabilization it was inferred that EqT-II increases membrane permeability by forming oligomeric channels comprising several copies of the cytolysin monomer. The existence of such oligomers was directly demonstrated by chemical cross-linking. Addition of EqT-II to one side of a planar lipid membrane (PLM) increases the conductivity of the film in discrete steps of defined amplitude indicating the formation of cation-selective channels. The conductance of the channel is consistent with the estimated size of the lesion formed in HRBC. High pH and sphingomyelin promoted the interaction even in this system. Chemical modification of lysine residues or carboxyl groups of this protein changed the conductance, the ion selectivity and the current-voltage characteristic of the pore, suggesting that both these groups were present in its lumen.     

Basic trypsin-subtilisin inhibitor from marine turtle egg white: Hydrodynamic and inhibitory properties

A basic trypsin-subtilisin inhibitor has been isolated from the egg white of marine turtle (Caretta caretta Linn.) and purified to homogeneity by gel filtration followed by ion-exchange chromatography. It has a single polypeptide chain of 117 amino acid residues, having a molecular weight of 13,600. It lacks methionine and tryptophan. Its isoelectric point is atpH 10.0 and the sedimentation coefficient (s_20,w) value of 1.62 S is independent of protein concentration. It has a Stokes radius of 18.8 Å, an intrinsic viscosity of 0.048 dl g^–1 and a diffusion coefficient of 10.17×10^–7 cm² sec^–1. Its fluorescence emission spectrum is similar to that of free tyrosine and the bimolecular quencing rate constant of its tyrosine residues with acrylamide is 3.15×10⁹ M^–1 sec^–1. The inhibitor strongly inhibits both trypsin and subtilisin by forming enzyme-inhibitor complexes at a molar ratio of unity. The nature of inhibition toward both enzymes is not temporary. It has independent binding sites for inhibition of trypsin and subtilisin. Chemical modification with tetranitromethane suggests the presence of three tyrosine residues on the surface of the inhibitor molecule.     

绿色木霉组蛋白去乙酰化酶编码基因TvRpd3在木霉生物防治作用中的功能分析

【目的】本文借助基因编辑技术在具有生物防治潜力的绿色木霉(Trichoderma viride)中敲除组蛋白去乙酰化酶编码基因TvRpd3,来研究TvRpd3基因及其编码蛋白在提高木霉病原菌拮抗能力中的作用。【方法】利用融合PCR和同源重组策略构建了TvRpd3基因缺失的突变菌株,通过对峙培养、表型观察、免疫组化检测、代谢组学分析等系统比较TvRpd3基因敲除前后菌株的组蛋白乙酰化修饰水平、次级代谢产物合成、病原菌拮抗能力以及田间防治效果等。【结果】与野生型菌株相比,缺失TvRpd3基因的木霉工程菌(?TvRpd3)对多种病原菌表现出了更强的对峙抑制效果,其所产的发酵液对小麦白粉病、烟草黑胫病和番茄枯萎病的防治效果分别提高了62.27%、57.45%和70.71%。同时,敲除TvRpd3基因也显著改变了木霉工程菌所产次级代谢产物的种类和产量,抗生性物质的产量大幅提高。【结论】绿色木霉TvRpd3基因及其介导的组蛋白乙酰化修饰在提高绿色木霉生物防治中起着重要作用。     

Refolding and proton pumping activity of a polyethylene glycol-bacteriorhodopsin water-soluble conjugate.

Bacteriorhodopsin (BR), from the purple membrane (PM) of Halobacterium halobium, was chemically modified with methoxypolyethylene glycol (m-PEG; molecular weight = 5,000 Da) succinimidyl carbonate. The polyethylene glycol-bacteriorhodopsin (m-PEG-SC-BR33) conjugate, containing one polyethylene glycol chain, was water soluble. The secondary structure of the conjugate in water appeared partially denatured, but was shown to contain alpha-helical segments by circular dichroism spectroscopy. The isolated bacteriorhodopsin conjugate, with added retinal, was refolded in a mixed detergent-lipid micelle and had an absorption maximum at 555 nm. The refolded conjugate was transferred into vesicles that pumped protons, upon illumination, as efficiently as did native BR. Modification of the PM with m-PEG did not alter the native structure or inhibit proton pumping, and therefore it is suggested that the glycol polymer is present as a moiety covalently linked to residues unnecessary for proton pumping and proper folding. The site of attachment of m-PEG was determined to be at either Lys 129 or Lys 159, with position Lys 129 the most probable site of attachment. The m-PEG-SC-BR33 could be stepwise refolded to the native conformation by the addition of trifluoroethanol to lower the dielectric constant, simulating the insertion of the BR into the phospholipid bilayer.     

Specificity and regulation of the mutator transposable element system in maize

The Mutator transposable element system is exceptional in many of its basic attributes. The high frequency and low specificity of mutant induction are both unusual and useful characteristics of the Mutator system. Other basic features are at least equally fascinating: the existence of multiple Mu element subfamilies with apparently unrelated internal sequences; the lack of correlation between Mu element transposition and excision; the complex inheritance of Mutator activity; the tight developmental regulation of Afufaror‐conditioned events; and the coordinated processes of element modification/inactivation, to name a few.

Molecular and genetic studies over the last 10 years have begun to explain many of these interesting properties and have uncovered new mysteries of Mutator biology. Both positive and negative regulators of the system have been identified and characterized to varying degrees. Insertion specificity has been observed at several levels. Recent accomplishments include the isolation of an autonomous Mu element and the discovery of maize lines with altered developmental regulation of Mutator‐derived mutability. This review defines the Mutator system, describes the status of current experimentation in the Mutator field, proposes models that may explain some aspects of Mutator behavior, and details future studies that will help elucidate the nature of the Mutator phenomenon.     

Floral sex ratio variation in hermaphrodites of gynodioeciousChionographis japonica var.kurohimensis Ajima et Satomi (Liliaceae)

Intrapopulation and interpopulation variations in floral sex ratio in hermaphrodites of gynodioeciousChionographis japonica var.kurohimensis (Liliaceae) were examined. The relative ratio of male flowers to total flowers (male and perfect flowers) decreased with plant size, suggesting size-dependent gender modification. The relative ratio of male flowers per population-basis is negatively correlated with the mean number of perfect flowers. Since the number of perfect flowers proportionally increased with plant size, populations showing low maleness consist of relatively bigger plants and are considered to be in high-quality environment. On the other hand, the relative ratio of male flowers per population basis is independent of female frequency in the population. Plasticity in gender expression probably plays an important role of maintenance of gynodioecy inC. japonica var.kurohimensis.     

A histidine binding protein ofEscherichia coli: a component of cystine binding protein ofEscherichia coli

Summary Commercially obtained cystine binding protein (CBP), an osmotic shock protein ofEscherichia coli, was studied in an effort to determine its binding characteristics. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS/PAGE) analysis of commercially obtained CBP showed three protein bands. N-terminal amino acid microsequencing and subsequent computer search revealed that the sequence of one of these proteins (25-kDa) was nearly identical to histidine binding protein (HisJ) ofSalmonella typhimurium. Purification of CBP by HPLC yielded four protein peaks, of which one bound histidine exclusively. Binding was maximal at pH 5.0 to 6.0, at 4°C, did not require calcium or magnesium ions and was not inhibited by reduction of CBP disulfide bonds. Amino acids other than histidine or cystine did not bind to CBP. These data show that commercially available CBP is not a homogenous protein; it contains a histidine as well as a cystine binding component.     

RhoB的翻译后修饰与细胞命运

RhoB作为Rho家族的一员,其生物学活性和蛋白质水平的调控与其他成员有着较大的不同,在肿瘤的发生发展中也起着独特的作用。RhoB作为抑癌蛋白在肿瘤的靶向治疗上受到越来越多的关注,然而在有些类型的肿瘤中RhoB却起着促进肿瘤生长的作用,其中的分子机理还不清楚,亟待研究阐明。可逆的翻译后修饰是快速与精细调控RhoB功能的重要分子机制,对于维持正常细胞的生长、抑制细胞的早期癌变及肿瘤的发生发展至关重要。本文就RhoB翻译后修饰的研究,特别是其泛素化和SUMO化修饰之间的转化在肿瘤细胞命运决定中的作用进行综述,以期为探索RhoB的调控与肿瘤发生发展的机制,以及以RhoB为靶点的癌症治疗提供线索和思路。