Effect of Reactive Oxygen Species on Myelin Membrane Proteins

Fresh myelin, isolated from brainstems of adult rats, was incubated in the presence of Cu2+ and H2O2. Electrophoretic analysis of the reisolated myelin membrane revealed a gradual loss of the protein moiety from the characteristic pattern and an increase in aggregated material appearing at the origin of the gel. The aggregation of proteins was time-dependent and was concomitant with the accumulation of lipid peroxidation products reactive with thiobarbituric acid. Furthermore, during the course of incubation, there was a gradual decrease in the amount of recovered light myelin and a quantitatively similar increase in heavier myelin subfractions. The aggregation of proteins seems not to be directly related to the buoyant densities of myelin fragments. The peroxidative damage to the myelin proteins may be an important contributor to pathochemistry of myelin sheath, in particular, and in general it implies the susceptibility of the protein moiety of cell membranes to oxygen-induced deterioration.     

Interactions of detrital particulates and plankton

Detrital particulates, i.e. inorganic and non-living organic material of colloidal size and larger, span ten orders of magnitude in size and are ubiquitous in inland waters. Interactions between plankton and detrital particulates are reciprocal. Release of dissolved organics by living organisms enter the particulate size fraction by flocculation on bubbles or adsorption to inorganic particles. Bacteria benefit from attachment to particles and are agents in the aggregation of particulates. Nutrients released by decaying plankton can support phytoplankton growth. Potentially toxic compounds adsorb to particulates and then can enter pelagic food webs or sediment. Material egested by zooplankton contributes to the detrital pool which in turn is a food source for zooplankton.     

Ultrastructural study of differentiation processes during aggregation of purified sponge archaeocytes

Archaeocytes from the spongeEphydatia fluviatilis were dissociated and then isolated on Ficoll density gradients. Their aggregation and reconstitution processes were studied by transmission electron microscopy to determine their capabilities for differentiation.Archaeocyte aggregates follow a well defined sequence of differentiation to generate the characteristic structures of a sponge. Pinacoderm is the first structure to be regenerated and appears progressively at the surface of the 12 h aggregates. Pinacocytes which have differentiated in archaeocyte aggregates are identical to native ones except that the nucleolus remains in most cells. The choanocytes appear only after 24 h by a two step process. First, small cells (choanoblasts) are formed from archaeocytes by mitosis. These cells then transform into fully differentiated choanocytes possessing collars and flagella. The early choanocyte chambers are small, irregular and randomly dispersed in the aggregates. Finally, collencytes and sclerocytes begin to appear just before the aggregates spread on the substrate.The differentiation of a suspension of pure archaeocytes is a unique model system to study sponge cell differentiation and has allowed us to demonstrate that archaeocytes isolated from developed sponges maintain the capacity to differentiate even though this capacity is not usually expressed.     

Observations on the cytolemma of the olfactory receptor cell in the newt

Summary The fine structure of the cytolemma of olfactory receptor cells in the newt was studied by the freeze-fracture replica method. Two kinds of receptor cells were recognized, namely ciliated cells (ciliary type) and non-ciliated cells (microvilli type). The cytolemma of olfactory knobs as well as their processes from both types of receptor cells showed an abundance of large membrane particles 80110Å in diameter. The large square aggregation of membrane particles, 0.1×0.1 m to 0.2×0.3 m in size, consisting of 50100 cuboidal subunits, were found in the cytolemma of the dendrite. A structural model of aggregation is presented. The soma of the receptor cell revealed large pitted membrane particles about 140Å in diameter. These particles are possibly the morphologic counterpart to ionophores which have been proposed by electrophysiological studies.     

Experimentally produced diploid-triploid mouse chimaeras develop up to adulthood

Spontaneous diploid-triploid chimaeras occur sporadically in various mammalian species including man, but so far have never been produced experimentally. In order to get a deeper insight into the developmental consequences of this anomaly, we have developed two procedures that enabled for the first time to produce routinely diploid-triploid embryos, foetuses, and animals in the mouse. These procedures are: (1) aggregation of cleaving diploid embryos with triploid embryos produced by suppression of the second polar body in zygotes, and (2) fusion of a haploid karyoplast with one blastomere of the two-cell diploid embryos. The first procedure yielded 23 living and 6 dead postimplantation embryos and foetuses (age: 8th-19th day) out of which 22 were chimaeric. In addition, three chimaeric neonates reached adulthood. Two animals were fertile, and one--an overt chimaera--was an infertile male. The rate of postimplantation development of aggregation chimaeras was normal or only slightly retarded, and with one exception the foetuses were morphologically normal. Generally, the highest contribution of the 3n component in extra-embryonic structures was noted in the yolk sac, and usually it was higher than its contribution to the organs of the body. Chimaerism was most often noted in the liver, the heart, the intestine, and the lungs. Participation of triploid cells to all tissues studied, both in the body and in extra-embryonic structures, appeared to decrease slightly as development progressed. The second procedure yielded 10 foetuses and 6 adults. Three foetuses were chimaeric. Six fertile adults were probably non-chimaeras: the triploid component was absent in the coat and in the blood.     

A cylinder-shaped double ribbon structure formed by an amyloid hairpin peptide derived from the beta-sheet of murine PrP: an X-ray and molecular dynamics simulation study

A structural model of the murine PrP small beta-sheet was obtained by synthesizing the RGYMLGSADPNGNQVYYRG peptide comprising the two beta-strands 127-133 and 159-164 linked by a four-residue sequence of high turn propensity. The DPNG turn sequence is a "short circuit" replacing the original protein sequence between the two strands. This 19-residue peptide spontaneously forms very long single fibrils as observed by electron microscopy. The X-ray diffraction patterns of a partially oriented sample reveals an average arrangement of the hairpin peptides into a structure which can be geometrically approximated by an empty-core cylinder. The hairpins are oriented perpendicular to the cylinder axis and a 130 A helix period is observed. Based on X-ray diffraction constraints and on more indirect general protein structure considerations, a precise and consistent fibril model was built. The structure consists of two beta-sheet ribbons wound around a cylinder and assembled into a single fibril with a hairpin orientation perpendicular to the fibril axis. Subsequent implicit and explicit solvent molecular dynamics simulations provided the final structure at atomic resolution and further insights into the stabilizing interactions. Particularly important are the zipper-like network of polar interactions between the edges of the two ribbons, including the partially buried water molecules. The hydrophobic core is not optimally compact explaining the low density of this region seen by X-ray diffraction. The present findings provide also a simple model for further investigating the sequence-stability relationship using a mutational approach with a quasi-independent consideration of the polar and apolar interactions.     

Cooperative Chewing in a Gregariously Developing Parasitoid Wasp, <Emphasis Type="BoldItalic">Melittobia digitata</Emphasis> Dahms,Is Stimulated by Structural Cues and a Pheromone in Crude Venom Extract

To disperse after mating, female Melittobia digitata Dahms (Hymenoptera: Eulophidae) tunnel through the walls of their hosts nest. We found that M. digitata use chemical and structural cues to identify locations for chewing exit holes. An experimental combination of milked venom and artificial pits on the inner surface of rearing containers elicited a stronger response than either stimulus alone. We suggest that the venom-associated cue may be a pheromone that facilitates mutual attraction, aggregation, and focused chewing, and that these behaviors may have arisen from behaviors associated with the initial stages of host attack. This apparently cooperative behavior promises insights into the possible evolutionary origins of components of eusocial behavior.     

环鸟苷酸依赖的蛋白激酶对心血管功能的调节作用

环鸟苷酸(cGMP)依赖的蛋白激酶(PKG)是一氧化氮-cGMP的主要细胞内受体,在哺乳动物细胞中分为PKG-I和PKG-II两型。在PKG介导的血管平滑肌舒张作用中,其主要通过活化细胞膜上的钙活化的钾通道(BK通道),磷酸化肌质网上的受磷蛋白(phospholamban,PLB)和三磷酸肌醇受体相关的PKG-I底物(IP3receptor-associated PKG-I substrate,IRAG),降低细胞内Ca2 浓度。PKG还可通过活化肌球蛋白轻链磷酸酶及抑制Rho激酶降低肌球蛋白对Ca2 敏感性。PKG调节血管平滑肌细胞的基因表达和表型调变,调节细胞增生。PKG活化以后还具有抑制血小板聚集,抑制心肌细胞肥大等功能。最近的研究证明,PKG的表达水平和活性改变与动脉粥样硬化和再狭窄、高血压、糖尿病心血管病变以及硝酸盐耐受等的发病机制有密切关系。     

Does structural and chemical divergence play a role in precluding undesirable protein interactions?

To understand the evolutionary forces establishing, maintaining, breaking, or precluding protein-protein interactions, a comprehensive data set of protein complexes has been analyzed to examine the overlap between protein interfaces and the most conserved or divergent protein surface areas. The most divergent areas tend to be found predominantly away from protein interfaces, although when found at interfaces, they are associated with specific lack of cross-reactivity between close homologues, like in antibody-antigen complexes. Moreover, the amino acid composition of highly variable regions is significantly different from any other protein surfaces. The variable regions present higher structural plasticity as a result of insertions and deletions, and favor charged over hydrophobic residues, a known strategy to minimize aggregation. This suggests that (1) a rapid rate of mutations at these regions might be continuously altering their properties, making difficult the coadaptation, in shape and chemical complementarity, to potential interacting partners; and (2) the existence of some form of selective pressure for variable areas away from interfaces to accumulate charged residues, perhaps as an evolutionary mechanism to increase solubility and minimize undesirable interactions within the crowded cellular environment. Finally, these results are placed into the context of the aberrant oligomerization of sickle-cell anemia hemoglobin and prion proteins.     

Early events in protein aggregation: molecular flexibility and hydrophobicity/charge interaction in amyloid peptides as studied by molecular dynamics simulations

In a previous article (Zbilut et al., Biophys J 2003;85:3544-3557), we demonstrated how an aggregation versus folding choice could be approached considering hydrophobicity distribution and charge. In this work, our aim is highlighting the mutual interaction of charge and hydrophobicity distribution in the aggregation process. Use was made of two different peptides, both derived from a transmembrane protein (amyloid precursor protein; APP), namely, Abeta(1-28) and Abeta(1-40). Abeta(1-28) has a much lower aggregation propensity than Abeta(1-40). The results obtained by means of molecular dynamics simulations show that, when submitted to the most "aggregation-prone" environment, corresponding to the isoelectric point and consequently to zero net charge, both peptides acquire their maximum flexibility, but Abeta(1-40) has a definitely higher conformational mobility than Abeta(1-28). The absence of a hydrophobic "tail," which is the most mobile part of the molecule in Abeta(1-40), is the element lacking in Abeta(1-28) for obtaining a "fully aggregating" phenotype. Our results suggest that conformational flexibility, determined by both hydrophobicity and charge effect, is the main mechanistic determinant of aggregation propensity.