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Mapping sequences in loops of nuclear DNA by their progressive detachment from the nuclear cage.

Cook, P R; Brazell, I A
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 11/07/1980 EN
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Nuclear DNA is organised into loops, probably by attachment to a supramolecular structure. We describe a method which enables us to map the position of sequences within a loop relative to the point of attachment. Nuclear DNA is isolated unbroken by lysing HeLa cells in 2M NaCl to release structures which retain many of the morphological features of nuclei. Their DNA is supercoiled and so must remain unbroken and looped during lysis. Nucleoids are digested to various degrees with a restriction endonuclease and the cages - and any associated DNA - sedimented free from unattached DNA. The cage-associated DNA is purified and completely fragmented using the same restriction endonuclease. Equal weights of fragmented DNA are separated by gel electrophoresis, transferred to a filter and the relative amounts of the alpha, beta and gamma globin genes on the filter determined by hybridisation to the appropriate probes. The alpha genes, unlike the beta and gamma genes, resist detachment from the cage and so must lie close to the point of attachment to the cage. Our ability to map these genes implies that sequences cannot be attached at random to the cage; rather, specific sequences must be attached, so looping the DNA.

Supramolecular structure of stacked and unstacked regions of the photosynthetic membranes of Prochloron sp., a prokaryote

Giddings, Thomas H.; Withers, Nancy W.; Staehelin, L. Andrew
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1980 EN
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Freeze-fracture replicas of the photosynthetic prokaryote Prochloron sp., collected at Coconut Island, Hawaii, show that the thylakoids are differentiated into stacked and unstacked regions much like the thylakoids of green algae and higher plants. On the exoplasmic (E) fracture face, the particle density is greater in stacked regions (≈3100 particles/μm2) than in unstacked regions (≈925 particles/μm2). On the complementary protoplasmic (P) fracture face, the particle density is lower in stacked regions (≈2265 particles/μm2 than in unstacked regions (≈4980 particles/μm2). The histogram of the diameters of E face particles in unstacked regions shows a single broad peak centered at 80 Å. In stacked regions, four distinct peaks, at 75, 105, 130, and 160 Å, are observed. These size classes are virtually identical to those found on E faces of thylakoids of the green alga Chlamydomonas and of greening pea chloroplasts. In the latter systems, the different size classes of E face particles are believed to represent photosystem II units surrounded by variable amounts of chlorophyll a/b light-harvesting complex. We propose that the same interpretation applies to the thylakoids of Prochloron, which contain a similar chlorophyll a/b complex. Our results add to the evidence supporting the view of the chlorophyll a/b complex as both a light-harvesting complex and a membrane adhesion factor. The similarity of the architecture of the thylakoids of Prochloron to that of green algal and plant chloroplasts also provides additional evidence of an evolutionary relationship between Prochloron and the chloroplasts of green plants.

Deficiency of Uncoupler-Stimulated Adenosine Triphosphatase Activity in Tightly Coupled Hepatoma Mitochondria

Pedersen, Peter L.; Eska, Terry; Morris, Harold P.; Catterall, William A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1971 EN
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Tightly coupled mitochondria from the well-differentiated hepatoma 7800 failed to exhibit a significant 2,4-dinitrophenol-activated ATPase activity at concentrations of uncoupler sufficient to completely inhibit oxidative phosphorylation. ATPase activity could not be maximally activated by uncoupling agents more potent than 2,4-dinitrophenol, such as carbonylcyanide p-trifluoromethoxyphenylhydrazone and 5-chloro, 3-tert-butyl, 2′-chloro, 4′-nitrosalicylanilide, nor by Mg++ after the following treatments: sonication, freezing, detergent lysis, and digestion with trypsin. Gel electrophoresis patterns of the membrane proteins of the hepatome mitochondria revealed neither an absence of any one of the three different types of ATPase subunits characteristic of the homogeneous enzyme purified from normal liver mitochondria, nor a deficiency of the oligomeric molecule. Taken together, these data strongly suggest that the supramolecular structure of the membrane ATPase complex of mitochondria from hepatoma 7800 is altered in such a way that its capacity for ATP hydrolysis is severely diminished.

Enzyme associations in T4 phage DNA precursor synthesis

Reddy, G. P. V.; Singh, A.; Stafford, M. E.; Mathews, C. K.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1977 EN
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A direct approach is described to the question: Are enzymes of DNA precursor synthesis organized into a supramolecular structure? This approach involved sedimentation analysis of several T4 phage-coded early enzyme activities in crude lysates of infected Escherichia coli. One-third to one-half of several activities tested—dCMP hydroxymethylase, dTMP synthetase, deoxynucleoside 5′-monophosphate kinase, deoxyuridine triphosphatase, and probably dCMP deaminase, but not dihydrofolate reductase or DNA polymerase—sedimented much more rapidly than expected from molecular weight. About 5% of the host cell nucleoside diphosphate kinase, known to participate in T4 DNA precursor synthesis, cosedimented with these activities. To show that this rapidly sedimenting material represents an organized enzyme complex rather than a nonspecific aggregate, we studied the kinetics of formation of dTTP with dUMP as the initial substrate. This three-step reaction sequence reached its maximal rate within a few seconds when catalyzed by enzymes in the aggregate, whereas an equivalent mixture of uncomplexed enzymes required nearly 20 min before dTTP synthesis reached its maximal rate. The effect of aggregation is evidently to decrease the volume into which intermediates are free to diffuse. Because there is reason to believe that intracellular concentration gradients of DNA precursors exist...

Supramolecular organization of the mammalian translation system.

Negrutskii, B S; Stapulionis, R; Deutscher, M P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/02/1994 EN
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Although evidence suggests that the protein synthetic machinery is organized within cells, this point has been difficult to prove because any organization that might exist is lost upon preparation of the cell-free systems usually used to study translation in vitro. To examine this process under conditions more representative of the intact cell, we have developed an active protein-synthesizing system using Chinese hamster ovary (CHO) cells permeabilized with the plant glycoside saponin. This procedure renders cells permeable to trypan blue and exogenous tRNA, but there is little release of endogenous macromolecules. Protein synthesis in this system proceeds at the same rate as that in intact cells and is about 40-fold faster than that in a cell-free system prepared from the same cells. Active protein synthesis in this system requires the addition of only Mg2+, K+, and creatine phosphate, with a small further stimulation by ATP and an amino acid mixture; no exogenous macromolecules are necessary. The proteins synthesized in this system are indistinguishable from those made by the intact cell, and the channeling of aminoacyl-tRNA observed in vivo is maintained. Our data suggest that the permeabilized cell system retains the protein-synthesizing capabilities of the intact cell and presumably its internal structure as well. Studies with this system demonstrate that the protein-synthesizing apparatus is highly organized and that its macromolecular components are not freely diffusible in mammalian cells.

Complementarity in the Supramolecular Design of Arenaviruses and Retroviruses Revealed by Electron Cryomicroscopy and Image Analysis†

Neuman, Benjamin W.; Adair, Brian D.; Burns, John W.; Milligan, Ronald A.; Buchmeier, Michael J.; Yeager, Mark
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /03/2005 EN
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Arenaviruses are rodent-borne agents of diseases, including potentially lethal human hemorrhagic fevers. These enveloped viruses encapsidate a bisegmented ambisense single-stranded RNA genome that can be packaged in variable copy number. Electron cryomicroscopy and image analysis of New World Pichinde and Tacaribe arenaviruses and Old World lymphocytic choriomeningitis virus revealed pleomorphic enveloped particles ranging in diameter from ∼400 to ∼2,000 Å. The surface spikes were spaced ∼100 Å apart and extended ∼90 Å from the maximum phospholipid headgroup density of the outer bilayer leaflet. Distinctive stalk and head regions extended radially ∼30 and ∼60 Å from the outer bilayer leaflet, respectively. Two interior layers of density apposed to the inner leaflet of the viral lipid bilayer were assigned as protein Z and nucleoprotein (NP) molecules on the basis of their appearance, spacing, and projected volume. Analysis of en face views of virions lacking the GP-C spikes showed reflections consistent with paracrystalline packing of the NP molecules in a lattice with edges of ∼57 and ∼74 Å. The structural proteins of retroviruses and arenaviruses assemble with similar radial density distributions, using common cellular components.

Idiotypic mimicry and the assembly of a supramolecular structure: An anti-idiotypic antibody that mimics taxol in its tubulin—microtubule interactions

Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 17/01/1995 EN
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The supramolecular organization of ovomucin. Biophysical and morphological studies.

Rabouille, C; Aon, M A; Muller, G; Cartaud, J; Thomas, D
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/03/1990 EN
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Ovomucin participates in the ovomucin-gel-forming properties because of its shape and its ability to interact in a specific spatial organization. Purified from chicken egg-white by exclusion chromatography with Sephacryl S-300 and Sepharose CL-2B and analysed by light-scattering, it exhibited an Mr of about 40 x 10(6). This large Mr can be explained by the aggregation of polymers that can be degraded into 3 x 10(6)-Mr fragments by reduction with dithiothreitol. The values for hydrodynamic parameters such as Mr, radius of gyration, hydrodynamic radius, mass per unit length and combinations of them suggested that ovomucin is a linear and highly flexible molecule conferring upon it a random-coil-like structure in 0.2 M-NaCl solution. Analysis of the ovomucin molecules by electron microscopy revealed its linear character but also indicated a lower Mr than that obtained in the light-scattering experiments. By temperature-induced non-specific aggregation of an ovomucin solution containing other globular egg proteins, an attempt was made to find out what conditions are required for gel formation and to examine the quality of aggregation that is obtained under these conditions. Results show that the viscosity of the solution did not increase after heat treatment. Apparently...

Supramolecular structure of tripeptidyl peptidase II from human erythrocytes as studied by electron microscopy, and its correlation to enzyme activity.

Macpherson, E; Tomkinson, B; Bålöw, R M; Höglund, S; Zetterqvist, O
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/11/1987 EN
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Tripeptidyl peptidase II is an extralysosomal serine peptidase of an unusually large size, i.e. Mr greater than 10(6) for the native enzyme and Mr 135000 for the subunit. The enzyme from human erythrocytes was studied by electron microscopy on samples negatively stained by ammonium molybdate. Two different structural representations of the purified enzyme were obtained, both with a length of about 50 nm, and consisting of repetitive substructures. Upon dialysis of the enzyme against a Tris/HCl buffer, the activity was gradually decreased. This decrease was shown to parallel the dissociation of the large enzyme structures into smaller ones, the smallest measuring 3 nm by 10 nm and apparently corresponding to the repetitive substructures. The results indicate that a large polymeric form of the enzyme is a prerequisite for full activity.

Electrically monitoring DNA repair by photolyase

DeRosa, Maria C.; Sancar, Aziz; Barton, Jacqueline K.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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Cyclobutane pyrimidine dimers are the major DNA photoproducts produced upon exposure to UV radiation. If left unrepaired, these lesions can lead to replication errors, mutation, and cell death. Photolyase is a light-activated flavoenzyme that binds to pyrimidine dimers in DNA and repairs them in a reaction triggered by electron transfer from the photoexcited flavin cofactor to the dimer. Using gold electrodes modified with DNA duplexes containing a cyclobutane thymine dimer (T<>T), here we probe the electrochemistry of the flavin cofactor in Escherichia coli photolyase. Cyclic and square-wave voltammograms of photolyase deposited on these electrodes show a redox signal at 40 mV versus normal hydrogen electrode, consistent with electron transfer to and from the flavin in the DNA-bound protein. This signal is dramatically attenuated on surfaces where the π-stacking of the DNA bases is perturbed by the presence of an abasic site below the T<>T, an indication that the redox pathway is DNA-mediated. DNA repair can, moreover, be monitored electrically. Exposure of photolyase on T<>T-damaged DNA films to near-UV/blue light leads to changes in the flavin signal consistent with repair, as confirmed by parallel HPLC experiments. These results demonstrate the exquisite sensitivity of DNA electrochemistry to perturbations in base pair stacking and the applicability of this chemistry to probe reactions of proteins with DNA.

Supramolecular structure and dynamics

Turro, Nicholas J.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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Human Immunodeficiency Virus Type 1 Virological Synapse Formation in T Cells Requires Lipid Raft Integrity

Jolly, Clare; Sattentau, Quentin J.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /09/2005 EN
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Human immunodeficiency virus type 1 (HIV-1) can spread directly between T cells by forming a supramolecular structure termed a virological synapse (VS). HIV-1 envelope glycoproteins (Env) are required for VS assembly, but their mode of recruitment is unclear. We investigated the distribution of GM1-rich lipid rafts in HIV-1-infected (effector) T cells and observed Env colocalization with polarized raft markers GM1 and CD59 but not with the transferrin receptor that is excluded from lipid rafts. In conjugates of effector T cells and target CD4+ T cells, GM1, Env, and Gag relocated to the cell-cell interface. The depletion of cholesterol in the infected cell dispersed Env and GM1 within the plasma membrane, eliminated Gag clustering at the site of cell-cell contact, and abolished assembly of the VS. Raft integrity is therefore critical for Env and Gag coclustering and VS assembly in T-cell conjugates.

Nanotubules Formed by Highly Hydrophobic Amphiphilic α-Helical Peptides and Natural Phospholipids

Furuya, Tomomi; Kiyota, Taira; Lee, Sannamu; Inoue, Tohru; Sugihara, Gohsuke; Logvinova, Anna; Goldsmith, Paul; Ellerby, H. Michael
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em /03/2003 EN
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We previously reported that the 18-mer amphiphilic α-helical peptide, Hel 13-5, consisting of 13 hydrophobic residues and five hydrophilic amino acid residues, can induce neutral liposomes (egg yolk phosphatidylcholine) to adopt long nanotubular structures and that the interaction of specific peptides with specific phospholipid mixtures induces the formation of membrane structures resembling cellular organelles such as the Golgi apparatus. In the present study we focused our attention on the effects of peptide sequence and chain length on the nanotubule formation occurring in mixture systems of Hel 13-5 and various neutral and acidic lipid species by means of turbidity measurements, dynamic light scattering measurements, and electron microscopy. We designed and synthesized two sets of Hel 13-5 related peptides: 1) Five peptides to examine the role of hydrophobic or hydrophilic residues in amphiphilic α-helical structures, and 2) Six peptides to examine the role of peptide length, having even number residues from 12 to 24. Conformational, solution, and morphological studies showed that the amphiphilic α-helical structure and the peptide chain length (especially 18 amino acid residues) are critical determinants of very long tubular structures. A mixture of α-helix and β-structures determines the tubular shapes and assemblies. However...

Penton Release from P22 Heat-Expanded Capsids Suggests Importance of Stabilizing Penton-Hexon Interactions during Capsid Maturation

Teschke, Carolyn M.; McGough, Amy; Thuman-Commike, Pamela A.
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em /04/2003 EN
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Bacteriophage assembly frequently begins with the formation of a precursor capsid that serves as a DNA packaging machine. The DNA packaging is accompanied by a morphogenesis of the small round precursor capsid into a large polyhedral DNA-containing mature phage. In vitro, this transformation can be induced by heat or chemical treatment of P22 procapsids. In this work, we examine bacteriophage P22 morphogenesis by comparing three-dimensional structures of capsids expanded both in vitro by heat treatment and in vivo by DNA packaging. The heat-expanded capsid reveals a structure that is virtually the same as the in vivo expanded capsid except that the pentons, normally present at the icosahedral fivefold positions, have been released. The similarities of these two capsid structures suggest that the mechanism of heat expansion is similar to in vivo expansion. The loss of the pentons further suggests the necessity of specific penton-hexon interactions during expansion. We propose a model whereby the penton-hexon interactions are stabilized through interactions of DNA, coat protein, and other minor proteins. When considered in the context of other studies using chemical or heat treatment of capsids, our study indicates that penton release may be a common trend among double-stranded DNA containing viruses.

Dehydron: A Structurally Encoded Signal for Protein Interaction

Fernández, Ariel; Scott, Ridgway
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em /09/2003 EN
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We introduce a quantifiable structural motif, called dehydron, that is shown to be central to protein-protein interactions. A dehydron is a defectively packed backbone hydrogen bond suggesting preformed monomeric structure whose Coulomb energy is highly sensitive to binding-induced water exclusion. Such preformed hydrogen bonds are effectively adhesive, since water removal from their vicinity contributes to their stability. At the structural level, a significant correlation is established between dehydrons and sites for protein complexation, with the HIV-1 capsid protein P24 complexed with antibody light-chain FAB25.3 providing the most dramatic correlation. Furthermore, the number of dehydrons in homologous similar-fold proteins from different species is shown to be a signature of proteomic complexity. The techniques are then applied to higher levels of organization: The formation of the capsid and its organization in picornaviruses correlates strongly with the distribution of dehydrons on the rim of the virus unit. Furthermore, antibody contacts and crystal contacts may be assigned to dehydrons still prevalent after the capsid has been assembled. The implications of the dehydron as an encoded signal in proteomics, bioinformatics...

Exciton Theory for Supramolecular Chlorosomal Aggregates: 1. Aggregate Size Dependence of the Linear Spectra

Prokhorenko, V. I.; Steensgaard, D. B.; Holzwarth, A. R.
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em /11/2003 EN
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The interior of chlorosomes of green bacteria forms an unusual antenna system organized without proteins. The steady-spectra (absorption, circular dichroism, and linear dichroism) have been modeled using the Frenkel Hamiltonian for the large tubular aggregates of bacteriochlorophylls with geometries corresponding to those proposed for Chloroflexus aurantiacus and Chlorobium tepidum chlorosomes. For the Cf. aurantiacus aggregates we apply a structure used previously (V. I. Prokhorenko., D. B. Steensgaard, and A. R. Holzwarth, Biophys. J. 2000, 79:2105–2120), whereas for the Cb. tepidum aggregates a new extended model of double-tube aggregates, based on recently published solid-state nuclear magnetic resonance studies (B.-J. van Rossum, B. Y. van Duhl, D. B. Steensgaard, T. S. Balaban, A. R. Holzwarth, K. Schaffner, and H. J. M. de Groot, Biochemistry 2001, 40:1587–1595), is developed. We find that the circular dichroism spectra depend strongly on the aggregate length for both types of chlorosomes. Their shape changes from “type-II” (negative at short wavelengths to positive at long wavelengths) to the “mixed-type” (negative-positive-negative) in the nomenclature proposed in K. Griebenow, A. R. Holzwarth, F. van Mourik, and R. van Grondelle...

Nanoscale Features of Fibronectin Fibrillogenesis Depend on Protein-Substrate Interaction and Cytoskeleton Structure

Pompe, Tilo; Renner, Lars; Werner, Carsten
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
EN
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Cell-reorganized fibronectin layers on polymer films providing a gradation of the binding strength between protein and substrate were analyzed by combined fluorescence and scanning force microscopy. The nanoscale fibronectin patterns exhibited paired parallel fibrils with characteristic spacings of 156, 233, 304, and 373 nm. These spacings depend on the interaction of fibronectin with the substrate: at enhanced fibronectin-substrate anchorage the cells form larger stress fibers, which are assembled by α-actinin cross-linked pairs of actin filaments subunits at the focal adhesions. A ubiquitous repeating unit of ∼71 nm was found within these characteristic distances. We conclude that the dimensions of the actin stress fibers reflect the binding strength of fibronectin to the polymer substrate and act—in turn—as a template for the reorganization of fibronectin into surface-bound nanofibrils with characteristic spacings. This explanation was confirmed by data showing the α-actinin/fibronectin colocalization.

Adsorption of Frog Foam Nest Proteins at the Air-Water Interface

Cooper, Alan; Kennedy, Malcolm W.; Fleming, Rachel I.; Wilson, Emma H.; Videler, Hortense; Wokosin, David L.; Su, Tsueu-ju; Green, Rebecca J.; Lu, Jian R.
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
EN
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The surfactant properties of aqueous protein mixtures (ranaspumins) from the foam nests of the tropical frog Physalaemus pustulosus have been investigated by surface tension, two-photon excitation fluorescence microscopy, specular neutron reflection, and related biophysical techniques. Ranaspumins lower the surface tension of water more rapidly and more effectively than standard globular proteins under similar conditions. Two-photon excitation fluorescence microscopy of nest foams treated with fluorescent marker (anilinonaphthalene sulfonic acid) shows partitioning of hydrophobic proteins into the air-water interface and allows imaging of the foam structure. The surface excess of the adsorbed protein layers, determined from measurements of neutron reflection from the surface of water utilizing H2O/D2O mixtures, shows a persistent increase of surface excess and layer thickness with bulk concentration. At the highest concentration studied (0.5 mg ml−1), the adsorbed layer is characterized by three distinct regions: a protruding top layer of ∼20 Å, a middle layer of ∼30 Å, and a more diffuse submerged layer projecting some 25 Å into bulk solution. This suggests a model involving self-assembly of protein aggregates at the air-water interface in which initial foam formation is facilitated by specific surfactant proteins in the mixture...

The Role of Phe in the Formation of Well-Ordered Oligomers of Amyloidogenic Hexapeptide (NFGAIL) Observed in Molecular Dynamics Simulations with Explicit Solvent

Wu, Chun; Lei, Hongxing; Duan, Yong
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
EN
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We observed fast aggregation of partially ordered oligomers in an earlier simulation study of an amyloidogenic hexapeptide NFGAIL. In this work, the nucleation of highly ordered oligomers was further investigated by a combined total of 960 ns molecular dynamics simulations with explicit solvent on NFGAIL and its nonamyloidogenic mutant NAGAIL. In these simulations, four dimer subunits that each was constrained by harmonic forces as a two-strand β-sheet were used to enhance the rate of formation. It was found that a critical role played by the aromatic residue Phe was to direct the stacking of β-sheets to form ordered multilayer aggregates. We also found that many molecular arrangements of the peptide satisfied the “cross-β-structure”, a hallmark of amyloid fibrils. The tendency for the peptide to form either parallel or antiparallel β-sheet was comparable, as was the tendency for the β-sheets to stack either in parallel or antiparallel orientation. Overall, ∼85% of the native hexapeptide formed octamers. The fact that only 8% of the octamers were well-ordered species suggests that the dissociation of the disordered oligomers be the rate-limiting step in the formation of highly ordered oligomers. Among the well-ordered subunit pairs...

The Effect of Salt on Self-Assembled Actin-Lysozyme Complexes

Guáqueta, Camilo; Sanders, Lori K.; Wong, Gerard C. L.; Luijten, Erik
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
EN
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We present a combined experimental and computational study of the bundling of F-actin filaments induced by lysozyme proteins. Synchrotron small-angle x-ray scattering results show that these bundles consist of close-packed columnar complexes in which the actin is held together by incommensurate, one-dimensional arrays of lysozyme macroions. Molecular dynamics simulations of a coarse-grained model confirm the arrangement of the lysozyme and the stability of this structure. In addition, we find that these complexes remain stable even in the presence of significant concentrations of monovalent salt. The simulations show that this arises from partitioning of the salt between the aqueous and the condensed phases. The osmotic pressure resulting from the excess concentration of the salt in the aqueous phase balances the osmotic pressure increase in the bundle. These results are relevant for a variety of biological and biomedical problems in which electrostatic complexation between anionic polyelectrolytes and cationic globular proteins takes place, such as the pathological self-assembly of endogenous antibiotic polypeptides and inflammatory polymers in cystic fibrosis.