Sulfated Polysaccharides as a Fighter with Protein Non-Physiological Aggregation: The Role of Polysaccharide Flexibility and Charge Density.

Proteins can lose native functionality due to non-physiological aggregation. In this work, we have shown the power of sulfated polysaccharides as a natural assistant to restore damaged protein structures. Protein aggregates enriched by cross-ß structures are a characteristic of amyloid fibrils related to different health disorders. Our recent studies demonstrated that model fibrils of hen egg white lysozyme (HEWL) can be disaggregated and renatured by some negatively charged polysaccharides. In the current work, using the same model protein system and FTIR spectroscopy, we studied the role of conformation and charge distribution along the polysaccharide chain in the protein secondary structure conversion. The effects of three carrageenans (κ, ι, and λ) possessing from one to three sulfate groups per disaccharide unit were shown to be different. κ-Carrageenan was able to fully eliminate cross-ß structures and complete the renaturation process. ι-Carrageenan only initiated the formation of native-like ß-structures in HEWL, retaining most of the cross-ß structures. In contrast, λ-carrageenan even increased the content of amyloid cross-ß structures. Furthermore, κ-carrageenan in rigid helical conformation loses its capability to restore protein native structures, largely increasing the amount of amyloid cross-ß structures. Our findings create a platform for the design of novel natural chaperons to counteract protein unfolding.

Alkyl triphenylphosphonium surfactants as nucleic acid carriers: complexation efficacy toward DNA decamers, interaction with lipid bilayers and cytotoxicity studies.

Herein, for the first time the complexation ability of a homological series of triphenylphosphonium surfactants (TPPB-n) toward DNA decamers has been explored. Formation of lipoplexes was confirmed by alternative techniques, including dynamic light scattering, indicating the occurrence of nanosized complexes (ca. 100-150 nm), and monitoring the charge neutralization of nucleotide phosphate groups and the fluorescence quenching of dye-intercalator ethidium bromide. The complexation efficacy of TPPB-surfactants toward an oligonucleotide (ONu) is compared with that of reference cationic surfactants. Strong effects of the alkyl chain length and the structure of the head group on the surfactant/ONu interaction are revealed, which probably occur via different mechanisms, with electrostatic and hydrophobic forces or intercalation imbedding involved. Phosphonium surfactants are shown to be capable of disordering lipid bilayers, which is supported by a decrease in the temperature of the main phase transition, Tm. This effect enhances with an increase in the alkyl chain length, indicating the integration of TPPB-n with lipid membranes. This markedly differs from the behavior of typical cationic surfactant cetyltrimethylammonium bromide, which induces an increase in the Tm value. It was demonstrated that the cytotoxicity of TPPB-n in terms of the MTT-test on a human cell line 293T nonmonotonically changes within the homological series, with the highest cytotoxicity exhibited by the dodecyl and tetradecyl homologs.

NMR structure, conformational dynamics, and biological activity of PsDef1 defensin from Pinus sylvestris.

Plants have developed a complex defense response system against pests and pathogens. Defensins, produced by plants as part of their innate immune response, form the family of small, basic, cysteine-rich proteins with activity primarily directed against fungal pathogens. In addition, plant defensins can show antibacterial activity and protease and insect amylase inhibitory activities. However, in gymnosperms, only antifungal activity of defensins has been described thus far. Here, we report antibacterial and insect α-amylase inhibition activities for defensin PsDef1 from P. sylvestris, the first defensin from gymnosperms with a broad range of biological activities described. We also report the solution NMR structure of PsDef1 and its dynamics properties assessed by a combination of experimental NMR and computational techniques. Collectively, our data provide an insight into structure, dynamics, and functional properties of PsDef1 that could be common between defensins from this taxonomic group.

Structural basis for regulation of stability and activity in glyceraldehyde-3-phosphate dehydrogenases. Differential scanning calorimetry and molecular dynamics.

Tissue specific isoforms of human glyceraldehyde-3-phosphate dehydrogenase, somatic (GAPD) and sperm-specific (GAPDS), have been reported to display different levels of both stability and catalytic activity. Here we apply MD simulations to investigate molecular basis of this phenomenon. The protein is a tetramer where each subunit consists of two domains - catalytic and NAD-binding one. We demonstrated key residues responsible for intersubunit and interdomain interactions. Effect of several residues was studied by point mutations. Overall we considered three mutations (Glu96Gln, Glu244Gln and Asp311Asn) disrupting GAPDS-specific salt bridges. Comparison of calculated interaction energies with calorimetric enthalpies confirmed that intersubunit interactions were responsible for enhanced thermostability of GAPDS whereas interdomain interactions had indirect influence on intersubunit contacts. Mutation Asp311Asn was around 10Å far from the active center and corresponded to the closest natural substitution in the isoenzymes. MD simulations revealed that this residue had slight interaction with catalytic residues but influenced the hydrogen bond net and dynamics in active site. These effects can be responsible for a strong influence of this residue on catalytic activity. Overall, our results provide new insight into glyceraldehyde-3-phosphate dehydrogenase structure-function relationships and can be used for the engineering of mutant proteins with modified properties and for development of new inhibitors with indirect influence on the catalytic site.

Dynamics and thermodynamic properties of CXCL7 chemokine.

Chemokines form a family of signaling proteins mainly responsible for directing the traffic of leukocytes, where their biological activity can be modulated by their oligomerization state. We characterize the dynamics and thermodynamic stability of monomer and homodimer structures of CXCL7, one of the most abundant platelet chemokines, using experimental methods that include circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy, and computational methods that include the anisotropic network model (ANM), molecular dynamics (MD) simulations and the distance constraint model (DCM). A consistent picture emerges for the effects of dimerization and Cys5-Cys31 and Cys7-Cys47 disulfide bonds formation. The presence of disulfide bonds is not critical for maintaining structural stability in the monomer or dimer, but the monomer is destabilized more than the dimer upon removal of disulfide bonds. Disulfide bonds play a key role in shaping the characteristics of native state dynamics. The combined analysis shows that upon dimerization flexibly correlated motions are induced between the 30s and 50s loop within each monomer and across the dimer interface. Interestingly, the greatest gain in flexibility upon dimerization occurs when both disulfide bonds are present, and the homodimer is least stable relative to its two monomers. These results suggest that the highly conserved disulfide bonds in chemokines facilitate a structural mechanism that is tuned to optimally distinguish functional characteristics between monomer and dimer.

Interaction of Uperin Peptides with Model Membranes: Molecular Dynamics Study.

The interaction of antimicrobial and amyloid peptides with cell membranes is a critical step in their activities. Peptides of the uperin family obtained from the skin secretion of Australian amphibians demonstrate antimicrobial and amyloidogenic properties. All-atomic molecular dynamics and an umbrella sampling approach were used to study the interaction of uperins with model bacterial membrane. Two stable configurations of peptides were found. In the bound state, the peptides in helical form were located right under the head group region in parallel orientation with respect to the bilayer surface. Stable transmembrane configuration was observed for wild-type uperin and its alanine mutant in both alpha-helical and extended unstructured forms. The potential of mean force characterized the process of peptide binding from water to the lipid bilayer and its insertion into the membrane, and revealed that the transition of uperins from the bound state to the transmembrane position was accompanied by the rotation of peptides and passes through the energy barrier of 4-5 kcal/mol. Uperins have a weak effect on membrane properties.

κ-Carrageenan Hydrogel as a Matrix for Therapeutic Enzyme Immobilization.

During the last few decades, polysaccharide hydrogels attract more and more attention as therapeutic protein delivery systems due to their biocompatibility and the simplicity of the biodegradation of natural polymers. The protein retention by and release from the polysaccharide gel network is regulated by geometry and physical interactions of protein with the matrix. In the present work, we studied the molecular details of interactions between κ-carrageenan and three lipases, namely the lipases from Candida rugosa, Mucor javanicus, and Rhizomucor miehei-which differ in their size and net charge-upon protein immobilization in microparticles of polysaccharide gel. The kinetics of protein release revealed the different capability of κ-carrageenan to retain lipases, which are generally negatively charged; that was shown to be in line with the energy of interactions between polysaccharides and positively charged epitopes on the protein surface. These data create a platform for the novel design of nanocarriers for biomedical probes of enzymatic origin.

Fibril fragments from the amyloid core of lysozyme: An accelerated molecular dynamics study.

Protein aggregation and formation of amyloid fibrils are associated with many diseases and present a ubiquitous problem in protein science. Hen egg white lysozyme (HEWL) can form fibrils both from the full length protein and from its fragments. In the present study, we simulated unfolding of the amyloidogenic fragment of HEWL encompassing residues 49-101 to study the conformational aspects of amyloidogenesis. The accelerated molecular dynamics approach was used to speed up the sampling of the fragment conformers under enhanced temperature. Analysis of conformational transformation and intermediate structures was performed. During the unfolding, the novel short-living and long-living ß-structures are formed along with the unstructured random coils. Such ß-structure enriched monomers can interact with each other and propagate into fibril-like forms. The stability of oligomers assembled from these monomers was evaluated in the course of MD simulations with explicit water. The residues playing a key role in fibril stabilization were determined. The work provides new insights into the processes occurring at the early stages of amyloid fibril assembly.

Rhizosphere Bacterium Rhodococcus sp. P1Y Metabolizes Abscisic Acid to Form Dehydrovomifoliol.

The phytohormone abscisic acid (ABA) plays an important role in plant growth and in response to abiotic stress factors. At the same time, its accumulation in soil can negatively affect seed germination, inhibit root growth and increase plant sensitivity to pathogens. ABA is an inert compound resistant to spontaneous hydrolysis and its biological transformation is scarcely understood. Recently, the strain Rhodococcus sp. P1Y was described as a rhizosphere bacterium assimilating ABA as a sole carbon source in batch culture and affecting ABA concentrations in plant roots. In this work, the intermediate product of ABA decomposition by this bacterium was isolated and purified by preparative HPLC techniques. Proof that this compound belongs to ABA derivatives was carried out by measuring the molar radioactivity of the conversion products of this phytohormone labeled with tritium. The chemical structure of this compound was determined by instrumental techniques including high-resolution mass spectrometry, NMR spectrometry, FTIR and UV spectroscopies. As a result, the metabolite was identified as (4RS)-4-hydroxy-3,5,5-trimethyl-4-[(E)-3-oxobut-1-enyl]cyclohex-2-en-1-one (dehydrovomifoliol). Based on the data obtained, it was concluded that the pathway of bacterial degradation and assimilation of ABA begins with a gradual shortening of the acyl part of the molecule.

Brownian dynamics simulation of substrate motion near active site of enzyme entrapped inside reverse micelle.

Brownian dynamics simulation has been applied to analyze the influence of the electrostatic field of a reverse micelle on the enzyme-substrate complex formation inside a micelle. The probability that the enzyme-substrate complex will form from serine protease (trypsin) and the specific hydrophilic cationic substrate Nalpha-benzoyl-L: -arginine ethyl ester has been studied within the framework of the encounter complex formation theory. It has been shown that surfactant charge, dipole moments created by charged surfactant molecules and counterions, and permittivity of the inner core of reverse micelles can all be used as regulatory parameters to alter the substrate orientation near the active site of the enzyme and to change the probability that the enzyme-substrate complex will form.

Structure of Scots pine defensin 1 by spectroscopic methods and computational modeling.

Defensins are part of the innate immune system in plants with activity against a broad range of pathogens, including bacteria, fungi and viruses. Several defensins from conifers, including Scots pine defensin 1 (Pinus sylvestris defensin 1, (PsDef1)) have shown a strong antifungal activity, however structural and physico-chemical properties of the family, needed for establishing the structure-dynamics-function relationships, remain poorly characterized. We use several spectroscopic and computational methods to characterize the structure, dynamics, and oligomeric state of PsDef1. The three-dimensional structure was modeled by comparative modeling using several programs (Geno3D, SWISS-MODEL, I-TASSER, Phyre(2), and FUGUE) and verified by circular dichroism (CD) and infrared (FTIR) spectroscopy. Furthermore, FTIR data indicates that the structure of PsDef1 is highly resistant to high temperatures. NMR diffusion experiments show that defensin exists in solution in the equilibrium between monomers and dimers. Four types of dimers were constructed using the HADDOCK program and compared to the known dimer structures of other plant defensins. Gaussian network model was used to characterize the internal dynamics of PsDef1 in monomer and dimer states. PsDef1 is a typical representative of P. sylvestris defensins and hence the results of this study are applicable to other members of the family.

Structural, biocomplexation and gene delivery properties of hydroxyethylated gemini surfactants with varied spacer length.

Gemini surfactants with hexadecyl tails and hydroxyethylated head groups bridged with tetramethylene (G4), hexamethylene (G6) and dodecamethylene (G12) spacers were shown to self-assemble at the lower critical micelle concentration compared to their conventional m-s-m analogs. The lipoplex formation and the plasmid DNA transfer into different kinds of host cells were studied. In the case of eukaryotic cells, high transfection efficacy has been demonstrated for DNA-gemini complexes, which increased as follows: G6G4>G12 has been obtained in the case of transformation of bacterial cells with plasmid DNA-gemini complexes, mediated by electroporation technique. Solely G6 shows transformation efficacy exceeding the control result (uncomplexed DNA), while the inhibitory effect occurs for G4 and G12. Analysis of physico-chemical features of single surfactants and lipoplexes shows that compaction and condensation effects change as follows: G6

On the relationship between the load and the variance of relative fitness.

BACKGROUND: Operation of natural selection can be characterized by a variety of quantities. Among them, variance of relative fitness V and load L are the most fundamental. RESULTS: Among all modes of selection that produce a particular value V of the variance of relative fitness, the minimal value L min of load L is produced by a mode under which fitness takes only two values, 0 and some positive value, and is equal to V/(1+V). CONCLUSIONS: Although it is impossible to deduce the load from knowledge of the variance of relative fitness alone, it is possible to determine the minimal load consistent with a particular variance of relative fitness. The concept of minimal load consistent with a particular biological phenomenon may be applicable to studying several aspects of natural selection.

On propagation of excitation waves in moving media: the FitzHugh-Nagumo model.

BACKGROUND: Existence of flows and convection is an essential and integral feature of many excitable media with wave propagation modes, such as blood coagulation or bioreactors. METHODS/RESULTS: Here, propagation of two-dimensional waves is studied in parabolic channel flow of excitable medium of the FitzHugh-Nagumo type. Even if the stream velocity is hundreds of times higher that the wave velocity in motionless medium (), steady propagation of an excitation wave is eventually established. At high stream velocities, the wave does not span the channel from wall to wall, forming isolated excited regions, which we called "restrictons". They are especially easy to observe when the model parameters are close to critical ones, at which waves disappear in still medium. In the subcritical region of parameters, a sufficiently fast stream can result in the survival of excitation moving, as a rule, in the form of "restrictons". For downstream excitation waves, the axial portion of the channel is the most important one in determining their behavior. For upstream waves, the most important region of the channel is the near-wall boundary layers. The roles of transversal diffusion, and of approximate similarity with respect to stream velocity are discussed. CONCLUSIONS: These findings clarify mechanisms of wave propagation and survival in flow.

Blood coagulation and propagation of autowaves in flow.

This study analyses the effect of flow and boundary reactions on spatial propagation of waves of blood coagulation. A simple model of coagulation in plasma consisting of three differential reaction-diffusion equations was used for numerical simulations. The vessel was simulated as a two-dimensional channel of constant width, and the anticoagulant influence of thrombomodulin present on the undamaged vessel wall was taken into account. The results of the simulations showed that this inhibition could stop the coagulation process in the absence of flow in narrow channels. For the used mathematical model of coagulation this was the case if the width was below 0.2 mm. In wider vessels, the process could be stopped by the rapid blood flow. The required flow rate increased with the increase of the damage region size. For example, in a 0.5-mm wide channel with 1-mm long damage region, the propagation of coagulation may be terminated at the flow rate of more than 20 mm/min.

A molecular-mechanical model of the microtubule.

Dynamic instability of MTs is thought to be regulated by biochemical transformations within tubulin dimers that are coupled to the hydrolysis of bound GTP. Structural studies of nucleotide-bound tubulin dimers have recently provided a concrete basis for understanding how these transformations may contribute to MT dynamic instability. To analyze these ideas, we have developed a molecular-mechanical model in which structural and biochemical properties of tubulin are used to predict the shape and stability of MTs. From simple and explicit features of tubulin, we define bond energy relationships and explore the impact of their variations on integral MT properties. This modeling provides quantitative predictions about the GTP cap. It specifies important mechanical features underlying MT instability and shows that this property does not require GTP-hydrolysis to alter the strength of tubulin-tubulin bonds. The MT plus end is stabilized by at least two layers of GTP-tubulin subunits, whereas the minus end requires at least one; this and other differences between the ends are explained by asymmetric force balances. Overall, this model provides a new link between the biophysical characteristics of tubulin and the physiological behavior of MTs. It will also be useful in building a more complete description of MT dynamics and mechanics.