Amino acid composition of parallel helix-helix interfaces

Amino acids at helix-helix parallel interfaces influence arrangement of helices and interhelical angles. Parallel interfaces in 79 proteins were considered. Location of amino acids at the positions analogous to a and d in GCN4 leucine zipper nomenclature shows that certain combinations of amino acids characteristic for parallel packing occur more often than could be expected by chance. Repeating sequence combinations occur at a and d positions of parallel helix-helix interfaces with similar values of interhelical angles not only in homologous proteins but also within the same protein and in nonhomologous proteins. Within each group of observed combinations correlation exists between the size of amino acid and magnitude of the interhelical angle.     

Specific sequence combinations at parallel and antiparallel helix-helix interfaces

Orientation of helices at parallel and antiparallel helix-helix interfaces in proteins depends on interacting amino acids from both helices. Particularly important are amino acids at positions analogous to a and d in GCN4 leucine zipper nomenclature, which form hydrophobic core. In this work repeating sequence combinations at a and d positions characteristic for both parallel and antiparallel packing are shown. Layer packing of hydrophobic groups is compared for possible combinations of aliphatic amino acids at all four positions. Correlation between specific position of methyl groups and interhelical angle is found for parallel and antiparallel types of packing.     

Classification of cortical neurons according to the character of their background impulse activity]

The method of basic components and cluster analysis was used to classify 75 units in the visual cortex of alert rabbits, proceeding from the empiric form of distribution of interspike intervals (DII), the mean frequency of impulsation and the relative number of intervals up to 500 msec. They were classified into nine groups containing from two to twelve units. Besides the cues, used as a basis for classification, the groups of units also differed in the structure of burst activity, the correlation of adjacent intervals and the ratio between the short (up to 20 to 60 msec) and long intervals. The latter served to make suggestions on the genetic affinity of bimodal DII to those with a bend on the waning after the maximum, and on the nature of formation of high frequency bursts and intervals exceeding 20 to 60 msec.     

The impairment of antitoxic antitetanus immunity due to the combined effect of radiation and heat

In experiments with mice a delay was noted in the development of secondary immune response to revaccination with a tetanic anatoxin after the combined effect of radiation and heat; the maximum antibody formation occurred at later times. The low level of antitoxins within the first 10 days after the combined effect of radiation and heat correlated with the low tetanus resistance of animals.     

The character of the background spike activity of cortical neurons under the influence of psychotropic drugs]

A comparison was made on alert rabbits between the nature of spike activity of normal cortical neurones and of those after a two-week daily administration of neuroleptics, namely chlorpromazine, trifluoperazine and haloperidol in 1 and 5 mg/kg doses. The groups of neurones did not differ in the mean frequency of firing. However, the use of the main components method and of cluster analysis showed considerable differences between neuronal activity following the action of neuroleptics and that in control animals. The most common effect of neuroleptics consisted in a reduction of the number of low frequency neurones with burst discharges and small dispersion of distribution of interspike intervals. Trifluoperazine and especially haloperidol differed from chlorpromazine in that they brought about an appearance of cortical neurones for which the distribution of interspike intervals had an almost symmetrical form and a mode of 80--170 msec. After the action of haloperidol about a third of the neurones had a mode up to 10 msec. An assumption has been made that the major effect of trifluoperazine and haloperidol consists in an increase in the reverberative activity of the brain.     

Heterogeneity of packing: structural approach.

Analysis of the heterogeneity of packing in proteins showed that different groups of the protein preferentially contribute to low- or high-density regions. Statistical distribution reveals the two preferable values for packing density in the form of two peaks. One peak occurs in the range of densities 0.55-0.65, the other occurs in the range 0.75-0.8. The high-density peak is originated primarily by high packing inside the hydrogen bonded backbone and to some extent by side chains. Polar/charged and apolar side chains both contribute to the low-density peak. The average packing density values of individual atomic groups significantly vary for backbone atoms as well as for side chain atoms. The carbonyl oxygen atoms of protein backbone and the end groups of side chains show lower packing density than the rest of the protein. The side-chain atomic groups of a secondary structure element when packed against the neighboring secondary structure element form stronger contacts with the side chains of this element than with its backbone. Analysis of the low-density regions around each buried peptide group was done for the set of proteins with different types of packing, including alpha-alpha, alpha-beta, and beta-beta packing. It was shown that cavities are regularly situated in the groove of secondary structure element packed against neighboring elements for all types of packing. Low density in the regions surrounding the peptide groups and the end groups of side chains can be explained by their positioning next to a cavity formed upon the association of secondary structure elements. The model proposed can be applied to the analysis of protein internal motions, mechanisms of cellular signal transduction, diffusion through protein matrix, and other events.     

Recent history of Lake Ladoga

Combined paleolimnological investigations of a 1.8 m sediment core from the deepest north-western part of Lake Ladoga show stratigraphic changes in granulometric and chemical composition, organic matter content, diatom species composition and chlorophyll a concentration. The sediment accumulation rate was calculated and 5 stages of lake history over the last 4 000 years were described. Changes in lake environment were mainly caused by changes in climate and lake water balance. Human impact on the lake was also traced.     

Zerumbone induced apoptosis in liver cancer cells via modulation of Bax/Bcl-2 ratio

Background  

Zerumbone is a cytotoxic component isolated from Zingiber zerumbet Smith, a herbal plant which is also known as lempoyang. This new anticancer bioactive compound from Z. zerumbet was investigated for its activity and mechanism in human liver cancer cell lines.     

<Emphasis Type="Italic">Pseudomonas Aeruginosa</Emphasis> bacteriophage SN: 3D-reconstruction of the capsid and identification of surface proteins by electron microscopy

The virulent Pseudomonas aeruginosa bacteriophage SN belongs to the PB1-like species of the Myoviridae family. The comparatively small (66,391 bp) DNA genome of this phage encodes 89 predicted open reading frames and the proteome involves more than 20 structural proteins. A 3D model of the phage capsid to approximately 18 Å resolution reveals certain peculiarities of capsomer structure typical of only this bacteriophage species. In the present work recombinant structural proteins SN gp22 and gp29 were expressed and purified; and specific polyclonal antibodies were obtained. Immuno-electron microscopy of purified phage SN using secondary gold-conjugated antibodies has revealed that gp29 forms a phage sheath, and gp22 decorates the capsid. Precise identification of multicopy major capsid proteins is essential for subsequent construction of gene-engineered phages bearing non-native peptides on their surfaces (phage display).     

Influence of Distamycin,Chromomycin, and UV-irradiation on Extraction of Histone H1 from Rat Liver Nuclei by Polyglutamic Acid

Rat liver nucleus histone H1 was fractionated by polyglutamic acid (PG) in the presence of distamycin A (DM) or chromomycin A3 (CM). In the absence of the antibiotics, PG extracts from the nuclei about half of the nuclear H1. DM or CM added to the nuclei in saturating concentrations weakens the binding potential of most of H1. Titration of nuclei with DM shows that the number of binding sites for DM in the nuclei is less than in isolated DNA by only 20-25%, and this dif- ference disappears after treatment of nuclei with PG. The lower CD value of DM complexes with nuclei compared to that of DM complexes with free DNA is evidence of a change in the DM-DNA binding mode in nuclear chromatin. About 25% of total histone H1 is sensitive only to DM and s~5% is sensitive only to CM. Half of the DM-sensitive H1 fraction seems to have a different binding mode in condensed compared relaxed chromatin. A small part of H1 (s~3%) remains tightly bound to the nuclear chromatin independent of the presence of the antibiotics. Subfraction H1A is more DM-sensitive and H1B is more CM-sensitive. UV irradiation of nuclei results in dose-dependent cross-linking of up to 50% of total H1, which is neither acid-extractable nor recovered during SDS electrophoresis. PG with DM extracts only about 3% of H1 from UV- stabilized chromatin. DM treatment of the nuclei before UV irradiation results in extraction of the whole DM-sensitive H1 fraction (s~25%), which in this case is not stabilized in the nucleus. A hypothesis on possible roles of the found H1 fractions in chromatin structural organization is discussed.