Study of the Influence of Humic Acid Macromolecules on the Structure of Erythrocytes of Some Animals by the Method of Absorption

Erythrocyte absorption spectra were obtained from fresh chicken, goose, and guinea pig blood in solutions with humic acids, isolated from brown coal, to study interactions between erythrocytes and humic acids (HA). It has been established that the addition of HA to erythrocytes leads to the differently directed shifts of Soret band maxima in the erythrocyte absorption spectrum. Thus, for a solution [guinea pig erythrocyte (1.5 × 1012 particle/l) + HA №1], this difference was Δλ = +3.3 nm (shortwave shift); for a solution [chicken erythrocyte (2 × 1012 particle/l) + HA №1], Δλ = −1.5 nm (longwave shift); and for a solution [goose erythrocyte (6 × 1011 particle/l) + HA №1], Δλ = +4.3 nm (shortwave shift). A comparison of the absorption spectra of guinea pig oxyhemoglobin with 2 HA samples indicates that at any erythrocyte concentrations, the positions of the Soret band maxima for various HA samples differ. The data obtained testify to the individual character of the interaction between erythrocyte membranes and HA macromolecules. Two hypotheses were proposed to account for the results obtained. (1) “Structural hypothesis.” In the framework of this hypothesis, the molecules of membrane-bound oxyhemoglobin are in erythrocyte volume and can undergo noticeable, structural changes due to the deformation of erythrocyte membrane. (2) “Complexing hypothesis.” In terms of this hypothesis, the observed shifts of the position of the Soret band maxima can be explained by the possible penetration of light HA fragments through erythrocyte membrane into the inner erythrocyte region. This can cause the formation of complexes (oxyhemoglobin-HA). In this case, the complex formation can involve both the free oxyhemoglobin molecules (HbO2) and the membrane-bound ones

Model DNA for investigation of mechanism of nucleotide excision repair

The living cell DNA is under permanent attack of a variety of exogenous and endogenous damaging factors. Nucleotide excision repair (NER) is main pathway which removes a wide variety of bulky DNA adducts formed by UV light, electrophilic environmental mutagens, and chemotherapeutic agents. NER process in mammalian cells consistently leads to the very specific excision of damaged DNA fragments 24–32 nucleotides in length. The following DNA repair synthesis and DNA ligation restore intact DNA helix. The main set of the genes inactivated in NER-deficient higher eukaryotic cells was identified; about 30 proteins are involved in the specific multi-subunit complexes responsible for NER process. The specific NER feature is wide substrate specificity and great difference of damages elimination efficiencies. A key limiting step in NER is damage recognition and verification. One of the advanced and upcoming approaches to NER process investigation is based on the application of model DNAs – artificial DNA structures, which are analogs of substrate or intermediates of the repair process. This article reviews our current knowledge concerning the model DNA design, synthesis and application as a tool for the NER process comprehensive study

Role of poly(ADP-ribose)polymerase 2 in DNA repair

Poly(ADP-ribosyl)ation is a posttranslational protein modification significant for the genomic stability and cell survival in response to DNA damage. Poly(ADP-ribosyl)ation is catalyzed by poly(ADP-ribose)polymerases (PARPs), which use NAD+ as a substrate, synthesize polymer of (ADP)-ribose (PAR) covalently attached to nuclear proteins including PARP themselves. PARPs constitute a large family of proteins, in which PARP1 is the most abundant and best-characterized member. In spite of growing body of PARPs’ role in cellular processes, PARP2, the closest homolog of PARP1, still remains poorly characterized at the level of its contribution to different pathways of DNA repair. An overview summarizes in vivo and in vitro data on PARP2 implication in specialized DNA repair processes, base excision repair and double strand break repair

Interaction of PARP2 with DNA structures mimicking DNA repair intermediates

Poly(ADP-ribosyl)ation is a posttranslational protein modification significant for the genomic stability and cell survival in response to DNA damage. Poly(ADP-ribosyl)ation is catalyzed by poly(ADP-ribose)polymerases (PARPs). Whereas the role of PARP1 in response to DNA damage has been widely illustrated, the contribution of another DNA-dependent PARP, PARP2, has not been studied so far. Aim. To find out specific DNA targets of PARP2. Methods. The EMSA and the PARP activity tests were used. Results. We evaluated Kd values of PARP2-DNA complexes for several DNA structures mimicking intermediates of different DNA metabolizing processes and tested these DNA as «activators» of PARP1 and PARP2 in poly(ADP-ribose) synthesis. Conclusions. Like PARP1, PARP2 does not show correlation between the activation efficiency and Kd values for DNA. PARP2 was activated most effectively in the presence of over5DNA

Computer simulation of the spatial structure of MUC 1 peptides capable of inhibiting apoptosis

Identification of new effective inhibitors of apoptosis is an important task for drug development for treatment of a number diseases including neurogenerative diseases. Initiation of apoptosis occurs via the formationof macromolecular protein complexes. In these complexes, activation of key enzymes in apoptosis, caspases, takes place. One of those macromolecular complexes is DISC (death- inducing signaling complex) playing a central role in the induction of the extrinsic apoptosis pathway. The adaptor protein FA DD has a major role in the formation of the DISC. Therefore, inhibitors of FA DD, preventing its function in the DISC, can act as potential drugs inhibiting apoptosis. Furthermore, the study of the mechanisms of action of these inhibitors is of great interest for understanding the mechanisms of the signal transduction pathways of apoptosis. It has been reported that a natural protein inhibitor of FA DD is mucin-type 1 glycoprotein (MUC1). In particular, two fragments of the primary structure of the cytoplasmic domain of MUC1 (MUC1- CD) are capable of inhibiting the binding of caspase-8 to FA DD. However, the three-dimensional structure of MUC1 has not been obtained yet. It complicates significantly the rational design of potential drugs on the basis of these peptides. In this context, the aim of the present study was in silico prediction ofthree-dimensional structures of MUC1-CD peptides corresponding to protein fragments (1-20 and 46-72), as well as analysis of their conformational properties. The main focus of the work was given to the peptide MUC1-CD (46-72), which is capable of binding to FA DD. Using the methods of molecular dynamics in the implicit water it was shown that the peptide MUC1-CD (46-72) can take conformations similar to the conformations of a number of fragments of the caspase-8 DED domain. It was found that  the structure of the peptide MUC1-CD (46-72) is similar to the spatial structure of at least four fragments of caspase-8. These results indicate that the molecular mechanism of the inhibitory activity of the peptide can be explained by competitive binding with FA DD due to the structural and conformational similarity with the fragments of the caspase-8 DED domain

Model-based dissection of CD95 signaling dynamics reveals both a pro- and antiapoptotic role of c-FLIPL

A systems biology–based approach shows that life and death decisions for cells depend on the stoichiometry of c-FLIP isoforms

Design and experimental validation of the action of small molecule-based inhibitors of the FADD protein

CD95 is one of the best studied members of the death receptor family. Activation of CD95 leads to the induction of the cell death programme, apoptosis, via formation of the death-inducing signaling complex (DISC). FA DD is a key adaptor protein for the formation of the C D95 DISC and activation of caspase-8 in the receptor complex. FA DD comprises the death domain and the death effector domain (DED). The death domain is essential for the interactions of FA DD with CD95, while DED is necessary for the recruitment of procaspase-8, -10 and the protein c-FLIP into the DISC. The search for the inhibitors that would block the interactions of FA DD with the other core proteins of the DISC is essential for the studies of the structure and function of this complex, investigation of the apoptosis mechanisms and development of new treatments for neurodegenerative diseases. In the course of this work, the screening for small inhibitors in silico that selectively interact with DED has been performed. For this purpose, the molecular modeling of the protein complexes and virtual screening of the potential inhibitors of FA DD has been performed. In addition, a new technology to test the activity of these inhibitors has been developed. The computational and experimental analysis performed allowed us to characterize the optimal conformation of the FA DD protein for the design of the small molecules that can bind in the region of amino acid residue Y25. We presume that further optimization of the structures of chemical compounds that can bind with the hydrophobic pocket next to the residue Y25 of FA DD will allow for the creation of the new perspective inhibitors of the programmed cell death

Human base excision repair enzymes apurinic/apyrimidinic endonuclease1 (APE1), DNA polymerase β and poly(ADP-ribose) polymerase 1: interplay between strand-displacement DNA synthesis and proofreading exonuclease activity

We examined interactions between base excision repair (BER) DNA intermediates and purified human BER enzymes, DNA polymerase β (pol β), apurinic/apyrimidinic endonuclease (APE1) and poly(ADP-ribose) polymerase-1 (PARP-1). Studies under steady-state conditions with purified BER enzymes and BER substrates have already demonstrated interplay between these BER enzymes that is sensitive to the respective concentrations of each enzyme. Therefore, in this study, using conditions of enzyme excess over substrate DNA, we further examine the question of interplay between BER enzymes on BER intermediates. The results reveal several important differences compared with data obtained using steady-state assays. Excess PARP-1 antagonizes the action of pol β, producing a complete block of long patch BER strand-displacement DNA synthesis. Surprisingly, an excess of APE1 stimulates strand-displacement DNA synthesis by pol β, but this effect is blocked by PARP-1. The APE1 exonuclease function appears to be modulated by the other BER proteins. Excess APE1 over pol β may allow APE1 to perform both exonuclease function and stimulation of strand-displacement DNA synthesis by pol β. This enables pol β to mediate long patch sub-pathway. These results indicate that differences in the stoichiometry of BER enzymes may regulate BER

Dynamics within the CD95 death-inducing signaling complex decide life and death of cells

CD95-mediated apoptotic and NF-κB signaling were described by a simple kinetic model. We used a model reduction technique to reduce the number of reactions from 92 to 23 while maintaining a good model fit.p43-FLIP, which is generated at the CD95 DISC by procaspase-8 cleavage, was found to be the link between the CD95 DISC and the NF-κB pathway. P43-FLIP interacts with the IKK complex and leads to its activation.The CD95 DISC complex acts as a signal processor that diverges signals into the apoptotic and NF-κB pathways depending on the amounts of specific DISC proteins.Life/death decisions in CD95 signaling are determined by c-FLIPL and procaspase-8 in a non-linear way