Changes in Na+,K(+)-ATPase structure induced by cation binding. Approach by Raman spectroscopy.

Raman analysis of Na+,K(+)-ATPase structural changes induced by cation binding reveals a slight decrease ( < 10%) of the alpha-helical content upon E1-E2 transition. Pronounced conformational changes of the enzyme are unlikely as the character of the environment of tyrosine residues remains unaltered. However, local changes can take place as evidenced by changes in tryptophan vibration at about 880 cm-1.     

杠杆状雄蕊及其进化生态学意义

对被子植物一类特化雄蕊——杠杆状雄蕊的结构多样性及其进化生态学意义进行了归纳总结。植物的花在进化过程中, 常会发生雄蕊群的改变, 包括雄蕊数目及其形态结构的变化, 同时雄蕊功能也会发生相应的适应性转变。杠杆状雄蕊是指结构特化为杠杆状或距状, 在传粉过程中具有类似杠杆功能的一类特化的雄蕊类型。目前, 已在唇形科不同亚科以及姜科6个属中发现杠杆状雄蕊, 根据其结构和形态发生方式总体上可分为2大类: 一类是唇形科中以鼠尾草属(Salvia)为代表的, 由2个可育雄蕊平行发育、药隔组织增长所形成的杠杆状雄蕊; 另一类是姜科植物中由一个可育雄蕊特化形成的带有距状附属体的雄蕊类型。在生态功能上, 两类雄蕊均能通过传粉者推动其距状下臂做杠杆运动进行传粉, 被认为是一种促进异交的传粉机制, 可通过精确传粉和花粉分发等途径影响植物的繁殖成功。杠杆状雄蕊在不同的类群中是独立起源与进化的; 仅在唇形科鼠尾草属中, 杠杆状雄蕊发生了3次独立进化, 而且它可能是触发该属物种适应性辐射的关键性状。将来需在宏观进化和微观进化两个水平深入探讨杠杆状雄蕊的进化生态学意义。     

Water Binding in Legume Seeds

The physical status of water in seeds has a pivotal role in determining the physiological reactions that can take place in the dry state. Using water sorption isotherms from cotyledon and axis tissue of five leguminous seeds, the strength of water binding and the numbers of binding sites have been estimated using van't Hoff analyses and the D'Arcy/Watt equation. These parameters of water sorption are calculated for each of the three regions of water binding and for a range of temperatures. Water sorption characteristics are reflective of the chemical composition of the biological materials as well as the temperature at which hydration takes place. Changes in the sorption characteristics with temperature and hydration level may suggest hydration-induced structural changes in cellular components.     

Further studies of a spring phytoplankton bloom in an enclosed experimental ecosystem

A detailed characterization is presented of the spring diatom bloom which occurred in the enclosed experimental ecosystem bags at Loch Ewe, Scotland, during March–April 1983. The nutrient condition and bacterial biomass of the water column, phytoplankton species distribution, gross biochemical composition and detailed lipid composition (lipid class, fatty acid and free sterol) of the phytoplankton are reported throughout the bloom period. The results are compared with results from previous years. The conclusions are that major changes take place in the biochemical composition of a rapidly growing diatom population which affect both the gross composition and also the more detailed lipid composition. Such changes can take place over a matter of days and appear to be very dependent upon available growth conditions. Both carbohydrate and lipids levels increase towards the end of the bloom as nitrate and silicate levels are depleted in the water. Neutral lipids are shown to be important lipid components of the phytoplankton populations and long-chain ω3 polyunsaturated fatty acids are found to be only minor components of the structural polar lipids. The fatty acid and sterol data are discussed in relation to present knowledge concerning phytoplankton lipid composition.     

Fluorescence of rhodopsins and its relation to primary processes of light energy transformation

A new area of the investigation of visual and bacterial rhodopsins--fluorescence spectroscopy of the pigments is discussed. Fluorescence properties are considered in relation to photochemical transformations of the pigments at low temperatures. A number of fluorescent states of the pigments are described. It is shown that the excited states of bacteriorhodopsin and visual rhodopsin are characterized by a series of common features. The analysis of general properties of the pigments excited states allows a conclusion that the singlet excited states take part in the photoreaction. The photoreaction scheme is discussed in which structural changes of the chromophore take place already in the excited state.     

The role of structural changes in T4 bacteriophage tail proteins

Conformational changes in bacteriophage tail proteins after heating and ionic strength alteration leading to dissociation of tail sheath have been studied using protein fluorescence, differential scanning microcalorimetry and electron microscopy methods. Autonomous structural changes in tube-baseplate proteins have been revealed. They take place under the same conditions as those which release the bonds holding the sheath protein subunits to those of the tube in isolated sheathed tails. The conformational changes in the tube-baseplates are reversible similarly to the process of assembly and disassembly of the extended sheath. Morphological changes in the tube have been found at the temperature above the transition registered by protein fluorescence but not by calorimetry. This suggests that revealed spectral alterations reflect changes in quaternary structure of tail tube in particular.     

Testosterone-dependent changes in vivo and in vitro in the structure of the renal glomeruli of the teleost Gasterosteus aculeatus L.

Summary During the reproductive period of the male stickleback, structural and functional changes of the kidney take place, both in the glomeruli and in the renal tubule cells. The structural changes in the glomeruli involve almost all glomerular components and point to a reduction of the glomerular filtration rate. The purpose of this study was to investigate whether these changes are controlled by testosterone, indirectly or directly. In vivo experiments demonstrated that exposure of immature castrates for 8 days to methyltestosterone leads to activation of mesangial cells and podocytes, to slight expansion of mesangial matrix and slight thickening of basal lamina. Observations on cultured renal tissue showed that two androgens, 11-ketotestosterone and methyl testosterone, are also able to stimulate the secretory activity of podocytes and mesangial cells in vitro. The results therefore indicate, that most glomerular changes in male sticklebacks during the reproductive season are directly effected by testosterone.     

Thermotropic structural rearrangements in blood plasma lipoproteins in ischemic heart disease

Structural properties of blood plasma lipoproteins (LP) from coronary heart disease (CHD) patients were examined. Substantial differences were found in the pattern of the heat-induced structural restitution of LP of all classes in health and disease. At the same time no such differences were discovered in lipids isolated from LP. In high density lipoproteins from the plasma of CHD patients, a decrease in the microenvironmental polarity was shown to take place at a depth of 8 A from the surface of LP. The data obtained indicate substantial changes in the structural organization of LP of all classes in CHD. It is assumed that these changes are consequent on the modification of apoproteins and/or protein-lipid interactions in LP.     

Recovery after damage to motor cortical areas

Until recently, the neural bases underlying recovery of function after damage to the cerebral cortex were largely unknown. Recent results from neuroanatomical and neurophysiological studies in animal models have demonstrated that after cortical damage, long-term and widespread structural and functional alterations take place in the spared cortical tissue. These presumably adaptive changes may play an important role in functional recovery.     

Multivariate statistical analysis of tissue basophils in acute radiation sickness

By means of mark scale estimation method, discriminant and factor analyses, changes in integral indices on the state of mast cells in the rat mesentery have been investigated in dynamics of medullary, intestinal and cerebral forms of an acute radiation sickness. The integral indices are calculated basing on the morphometric parameters of the cells, that are obtained after the histological preparations are treated in a special automatic system for analysing images. At the medullary form of the acute radiation sickness, the greatest structural rearrangements of the mast cells take place during the first hours after the radiation, as well as during the climax of the disease, at the intestinal form, the analogous changes are revealed 1-3 days after the effect, and at the cerebral form--3 h after the radiation. The integral indices, calculated by means of the three methods, are well correlated with each other.     

Myosin-V motility: these levers were made for walking

Myosin-Va, a processive actin-based motor thought to be involved in organelle transport, now stands ready to join myosin-II (from muscle) as one of the most highly characterized members of the myosin superfamily. Recent reports from the laboratories of Goldman and colleagues and Selvin and colleagues have provided unprecedented, high-resolution views of the structural changes that take place while this motor moves along its track. Taken together, the new results indicate that myosin-Va tilts its light chain binding domains to 'walk' along actin in a hand-over-hand fashion.     

Structures of perfringolysin O suggest a pathway for activation of cholesterol-dependent cytolysins

Cholesterol-dependent cytolysins (CDCs), a large family of bacterial toxins, are secreted as water-soluble monomers and yet are capable of generating oligomeric pores in membranes. Previous work has demonstrated that large scale structural rearrangements occur during this transition but the detailed mechanism by which these changes take place remains a puzzle. Despite evidence of structural and functional couplings between domains 3 and 4, the crystal structure of the CDC, perfringolysin O (PFO), shows the two domains do not make direct contact. Here, we present crystal structures of PFO that demonstrate movements of domain 4 are sufficient to trigger conformational changes that are transmitted through the molecule to the distant domain 3. These coupled movements result in a loss of many contacts between domain 3 and rest of the molecule that would eventually lead to the exposure of transmembrane regions in preparation for membrane insertion. The structures reveal a detailed molecular pathway that may be the basis for the allosteric transition that occurs on initial membrane binding leading to the exposure of membrane-spanning regions in a domain distant from the initial site of interaction.     

The mechanism of pore formation by bacterial toxins

A remarkable group of proteins challenge the notions that protein sequence determines a unique three-dimensional structure, and that membrane and soluble proteins are very distinct. The pore-forming toxins typically transform from soluble, monomeric proteins to oligomers that form transmembrane channels. Recent structural studies provide ideas about how these changes take place. The recently solved structures of the beta-pore-forming toxins LukS, varepsilon-toxin and intermedilysin confirm that the pore-forming regions are initially folded up on the surfaces of the soluble precursors. To create the transmembrane pores, these regions must extend and refold into membrane-inserted beta-barrels.     

Chromatin reorganization during senescence of proliferating cells.

It was previously proposed (Macieira-Coelho, 1979) that aging of proliferating cells is the result of genome reorganization taking place during the division cycle. This hypothesis was investigated and a reorganization could indeed be ascertained in the different hierarchical orders of DNA structure; a correlation was found between changes in chromatin organization and the impairment of cell cycle-related events. Indeed, like the latter, the reorganization of chromatin structure is characterized by a succession of subtle changes through the cell population life span, and a final short stage with abrupt events. The final events seem to concern mainly the organization of heterochromatin. The reorganization in the genome is accompanied by structural changes in the cellular scaffold and an evolution of cell morphology. The remodeling occurring in the cell through serial divisions seems to take place in such a way as to decrease the probability of further reorganizations, tending to a limit. The decline of the proliferative activity seems to be the result of the tendency to reach this limit.     

核基质与细胞凋亡

阐述了凋亡过程中,核基质所发生的形态、生化变化及相关凋亡基因的表达,尤其是凋亡早期便出现核基质蛋白的降解.核基质是细胞核最基本的组分,对维持细胞核形态结构和功能非常重要,其主要由核纤层,核内骨架及核孔复合体构成,在DNA复制、转录、RNA加工转运等事件中起支持作用.多少年来,关于凋亡时细胞核形态及生化改变的分子机理一直未阐明,最近对核基质与细胞凋亡的研究取得了重大进展.     

Change in conformation of proteins in aqueous solutions of heterofunctional nonelectrolytes]

In narrow ranges of concentrations of heterofunctional nonelectrolytes in aqueous solutions, structural transitions occur, which manifest themselves in the self-association of nonelectrolytes molecules and are accompanied by the screening of their hydrophobic groups from the contact with the solvent. In the same nonelectrolytes concentration ranges, conformational changes of protein molecules in solutions take place. The compatibility of the concentration ranges of these two processes is due to the fact that when nonelectrolytes molecules are extruded from the network of hydrogen bonds during the structural transition, both the self-association of nonelectrolytes molecules and their incorporation into the hydrate shell of the protein occur. The dehydration of the protein results in the disturbance of the balance of intra- and intermolecular interactions maintaining the native protein structure, which leads to the rearrangement of the macromolecule conformation.     

Modulating crossover positioning by introducing large structural changes in chromosomes

Background

Crossing over assures the correct segregation of the homologous chromosomes to both poles of the dividing meiocyte. This exchange of DNA creates new allelic combinations thus increasing the genetic variation present in offspring. Crossovers are not uniformly distributed along chromosomes; rather there are preferred locations where they may take place. The positioning of crossovers is known to be influenced by both exogenous and endogenous factors as well as structural features inherent to the chromosome itself. We have introduced large structural changes into Arabidopsis chromosomes and report their effects on crossover positioning.

Results

The introduction of large deletions and putative inversions silenced recombination over the length of the structural change. In the majority of cases analyzed, the total recombination frequency over the chromosomes was unchanged. The loss of crossovers at the sites of structural change was compensated for by increases in recombination frequencies elsewhere on the chromosomes, mostly in single intervals of one to three megabases in size. Interestingly, two independent cases of induced structural changes in the same chromosomal interval were found on both chromosomes 1 and 2. In both cases, compensatory increases in recombination frequencies were of similar strength and took place in the same chromosome region. In contrast, deletions in chromosome arms carrying the nucleolar organizing region did not change recombination frequencies in the remainder of those chromosomes.

Conclusions

When taken together, these observations show that changes in the physical structure of the chromosome can have large effects on the positioning of COs within that chromosome. Moreover, different reactions to induced structural changes are observed between and within chromosomes. However, the similarity in reaction observed when looking at chromosomes carrying similar changes suggests a direct causal relation between induced change and observed reaction.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1276-z) contains supplementary material, which is available to authorized users.     

Coagulocyte alterations in clotting hemolymph of Carausius morosus L.

1. The structural changes in the coagulocytes of Carausius morosus during hemolymph coagulation in vitro have been studied under the PCM and in the TEM. 2. In agreement with former PCM observations on Carausius morosus, the coagulocytes are the only hemocytes to induce coagulation of the plasma. Immediately or after a few seconds upon withdrawal of the hemolymph, their structural changes consist of a considerable enlargement of the perinuclear cysterna and of direct ejection into the plasma of nuclear and cytoplasmic substances through microruptures of the cytoplasmic membrane. The other categories of hemocytes do not contribute to the plasma coagulation. Their structural alterations take place without breakage of the cytoplasmic membrane when the plasma reactions are already established. 4. These plasma reactions appear in the form of circular islands of granular material around the coagulocytes, of extension of the coagulum in the channels between the islands and of transformation of the clot into a network of threads. 5. As reported in other studies in the TEM, no specific organelle characteristic of the coagulocyte ultrastructure could be found in the coagulocytes of Carausius. 6. Owing to the absence of any specific structural criterion of identification, the results suggest that the functional difference between coagulocytes and the other categories of hemocytes as regards coagulation of the plasma might be caused in part by differences of permeability of the cell membranes.     

High pressure reveals that the stability of interdimeric contacts in the R- and T-state of HbA is influenced by allosteric effectors: Insights from computational simulations

The molecular details of the mechanism of action of allosteric effectors on hemoglobin oxygen affinity are not clearly understood. The global allostery model proposed by Yonetani et al. suggests that the binding of allosteric effectors can take place both in the R and T states and that they influence oxygen affinity through inducing global tertiary changes in the subunits. Recently published high pressure studies yielded dissociation constants at atmospheric pressure that showed a stabilizing effect of heterotropic allosteric effectors on the dimer interface in the R state, and a more pronounced destabilizing effect in a T state model. In the present work, we report on computational modeling used to interpret the high pressure experimental data. We show structural changes in the hemoglobin interdimeric interfaces, indicative of a global tertiary structural change induced by the binding of allosteric effectors. We also show that the number of water molecules bound at the interface is significantly influenced by binding effectors in the T state in accordance with the experimental data. Our results suggest that the binding of effectors at definite sites leads to tertiary changes that propagate to the interfaces and results in overall structural re-organizations.     

Structural aspects of AMPA receptor activation, desensitization and deactivation

Glutamate mediates most of the excitatory neurotransmission in the mammalian central nervous system by activating ionotropic glutamate receptors. Structural and functional studies of ionotropic glutamate receptors have offered detailed insight into the mechanism by which these integral membrane proteins function. In particular, advances in our understanding of the atomic structure of the agonist-binding domain have provided new opportunities to consider the conformational changes that take place in a functioning ligand-gated ion channel. Several recent studies have turned up important new ideas about the structural determinants of channel activation, deactivation and desensitization of AMPA receptors. Working hypotheses derived from this structural insight offer a rare opportunity to enrich and guide functional studies.