Regulation of Aggregation of Self-Associated Peptides,Including N-Terminal Fragments of the Alzheimer’s β-Amyloid Peptide,by Nitro Derivatives of Azoloazine

Russian Journal of Bioorganic Chemistry - The potential of the nitro compounds of the azoloazine class as regulators of aggregation of natural self-associating peptides was demonstrated by the...     

Levels of the Hierarchical Organization of Protein Sequences: An Analysis of Entropy Characteristics

Biophysics - A set of 24 647 nonhomologous protein sequences was examined. A pentapeptide occurrence profile was constructed for each sequence and hierarchically organized elements of various sizes...     

Effect of Ca2+ ions on hydrodynamic properties of pentamer and decamer of C-reactive protein in solution

The molecular mass and sedimentation coefficient of native C-reactive protein in solution were determined by analytical ultracentrifugation in the presence and absence of calcium ions. Pentameric C-reactive protein was shown to be the major macroscopic form of this protein in solution. The removal of calcium ions from solution caused decompaction of the protein accompanied by changes in its hydrodynamic parameters. The sedimentation coefficient s20(0), w of pentameric C-reactive protein in solution containing 2 mM--Ca2+ (6.6S) exceeded that for C-reactive protein in solution containing 2 mM EDTA (6.4S). Analysis of average molecular masses Mw and Mz obtained from sedimentation data demonstrated that the solution of highly purified protein was not homogeneous. As shown by intermolecular crosslinking, the solution also contained the 241-kDa decamer of C-reactive protein (9.5S) as a separate macroscopic form, whose share hardly reached 10% in the presence of 2 mM Ca2+ and increased after removal of calcium ions. The decamers were shown to result from intermolecular association of the pentamers.     

Anti-plasminogen autoantibodies from plasma of patients with systemic lupus erythematosus having anti-phospholipid antibody syndrome: isolation and some immunochemical properties

Blood plasma samples from patients with systemic lupus erythematosus having the anti-phospholipid antibody syndrome were found to contain anti-plasminogen antibodies of the IgG class. The titers of anti-plasminogen autoantibodies of the IgG class were elevated in these patients compared with normal controls. Part of the pool of IgG anti-plasminogen antibodies reacts with an epitope in the lysine-binding sites of plasminogen. Anti-plasminogen IgG isolated from patients' blood plasma is specific only for a native epitope of human plasminogen passively adsorbed on immunosorbent micro-titration plate. As shown by enzyme immunoassay, autoantibodies to plasminogen of the IgG class cross-react with human fibrinogen.     

Hypersensitivity of Escherichia coli Delta(uvrB-bio) mutants to 6-hydroxylaminopurine and other base analogs is due to a defect in molybdenum cofactor biosynthesis

We have shown previously that Escherichia coli and Salmonella enterica serovar Typhimurium strains carrying a deletion of the uvrB-bio region are hypersensitive to the mutagenic and toxic action of 6-hydroxylaminopurine (HAP) and related base analogs. This sensitivity is not due to the uvrB excision repair defect associated with this deletion because a uvrB point mutation or a uvrA deficiency does not cause hypersensitivity. In the present work, we have investigated which gene(s) within the deleted region may be responsible for this effect. Using independent approaches, we isolated both a point mutation and a transposon insertion in the moeA gene, which is located in the region covered by the deletion, that conferred HAP sensitivity equal to that conferred by the uvrB-bio deletion. The moeAB operon provides one of a large number of genes responsible for biosynthesis of the molybdenum cofactor. Defects in other genes in the same pathway, such as moa or mod, also lead to the same HAP-hypersensitive phenotype. We propose that the molybdenum cofactor is required as a cofactor for an as yet unidentified enzyme (or enzymes) that acts to inactivate HAP and other related compounds.     

Molybdenum cofactor-dependent resistance to N-hydroxylated base analogs in Escherichia coli is independent of MobA function

Lack of molybdenum cofactor (MoCo) in Escherichia coli and related microorganisms was found to cause hypersensitivity to certain N-hydroxylated base analogs, such as HAP (6-N-hydroxylaminopurine). This observation has lead to a previous proposal that E. coli contains a molybdoenzyme capable of detoxifying such N-hydroxylated analogs. Here, we show that, unexpectedly, deletion of all known or putative molybdoenzymes in E. coli failed to reveal any base-analog sensitivity, suggesting that a novel type of MoCo-dependent activity is involved. Further, we establish that protection against the analogs does not require the common molybdopterin guanine-dinucleotide (MGD) form of the cofactor, but instead the guanosine monophosphate (GMP)-free version of MoCo (MPT) is sufficient.     

A direct introduction of <Superscript>18</Superscript>O isotopes into peptides and proteins for quantitative mass spectroscopy analysis

A method for direct introduction of ¹⁸O isotopes into carboxyl groups of peptides and proteins via the exchange with H₂ ¹⁸O in the presence of TFA is described. The isotope label is sufficiently stable in a wide pH range. Since the compounds labeled by this method retain their physicochemical characteristics, they can be used as an internal standard in quantitative assay of authentic compounds in the analyzed objects by means of mass spectrometry. This method is applicable to quantitative analysis of peptides and proteins in biological environments, as well as for quantitative kinetic studies of metabolism and enzyme activity. The quantitative analysis of polypeptides and proteins is combined with trypsinolysis. When necessary, the isotope label can be simultaneously introduced into all peptides and proteins in a control biosample, making it applicable as a standard for comparative analysis of experimental biosamples.     

The Mechanism of Nucleotide Excision Repair-Mediated UV-Induced Mutagenesis in Nonproliferating Cells

Following the irradiation of nondividing yeast cells with ultraviolet (UV) light, most induced mutations are inherited by both daughter cells, indicating that complementary changes are introduced into both strands of duplex DNA prior to replication. Early analyses demonstrated that such two-strand mutations depend on functional nucleotide excision repair (NER), but the molecular mechanism of this unique type of mutagenesis has not been further explored. In the experiments reported here, an ade2 adeX colony-color system was used to examine the genetic control of UV-induced mutagenesis in nondividing cultures of Saccharomyces cerevisiae. We confirmed a strong suppression of two-strand mutagenesis in NER-deficient backgrounds and demonstrated that neither mismatch repair nor interstrand crosslink repair affects the production of these mutations. By contrast, proteins involved in the error-prone bypass of DNA damage (Rev3, Rev1, PCNA, Rad18, Pol32, and Rad5) and in the early steps of the DNA-damage checkpoint response (Rad17, Mec3, Ddc1, Mec1, and Rad9) were required for the production of two-strand mutations. There was no involvement, however, for the Pol η translesion synthesis DNA polymerase, the Mms2-Ubc13 postreplication repair complex, downstream DNA-damage checkpoint factors (Rad53, Chk1, and Dun1), or the Exo1 exonuclease. Our data support models in which UV-induced mutagenesis in nondividing cells occurs during the Pol ζ-dependent filling of lesion-containing, NER-generated gaps. The requirement for specific DNA-damage checkpoint proteins suggests roles in recruiting and/or activating factors required to fill such gaps.     

On the problem of dehydration and intracellular crystallization during freezing of cell suspensions.

The kinetic equation of the process of cell dehydration during freezing has been obtained. It is used to assess the degree of protoplasmic supercooling as a function of the cooling rate and cell parameters.The suggested model of dehydration cannot be applied to cells with permeability coefficients for water molecules more than 10^?5 cm/sec · bar, in particular to erythrocytes.The peculiarities of intracellular crystallization in red cells have been studied. The results show that red cells are likely to start freezing at cooling rates slower than those supposed from calculations of Mazur (9).