13,378 research outputs found
RECONSTITUTION OF ALLOPHYCOCYANIN FROM Mastigocladus laminosus WITH ISOLATED LINKER POLYPEPTIDE
No full textThe core linker polypeptide Lc 8.9 was isolated from Mastigocladus laminosus and purified on a preparative scale. A method for the reconstitution of allophycocyanin (AP)—linker complexes from isolated polypeptides was developed. The complex (αAP(βAP)3 Lc 8.9 was reconstituted and compared to (αAPβAP) and (αAPβAP)3 by sucrose density gradient ultracentrifugation, absorption, fluorescence emission and circular dichroism spectroscopy. Differences in the spectra of reconstituted and of directly isolated AP complexes are discussed
Fine mapping of posttranslational modifications of the linker histone H1 from Drosophila melanogaster.
No full textThe linker histone H1 binds to the DNA in between adjacent nucleosomes and contributes to chromatin organization and transcriptional control. It is known that H1 carries diverse posttranslational modifications (PTMs), including phosphorylation, lysine methylation and ADP-ribosylation. Their biological functions, however, remain largely unclear. This is in part due to the fact that most of the studies have been performed in organisms that have several H1 variants, which complicates the analyses. We have chosen Drosophila melanogaster, a model organism, which has a single H1 variant, to approach the study of the role of H1 PTMs during embryonic development. Mass spectrometry mapping of the entire sequence of the protein showed phosphorylation only in the ten N-terminal amino acids, mostly at S10. For the first time, changes in the PTMs of a linker H1 during the development of a multicellular organism are reported. The abundance of H1 monophosphorylated at S10 decreases as the embryos age, which suggests that this PTM is related to cell cycle progression and/or cell differentiation. Additionally, we have found a polymorphism in the protein sequence that can be mistaken with lysine methylation if the analysis is not rigorous
Preparation of Protein Conjugates via Homobifunctional Diselenoester Cross-Linker
No full textAdipic acid diselenoester
was developed as an efficient cross-linker
for covalent protein conjugation with a variety of small molecular
haptens, including mono- and disaccharides, peptide, fluorescence
dye, and nicotine. Compared to the counterparts of N-hydroxysuccinimide (NHS) and p-nitrophenyl (PNP)
linkers, the diselenoester linker demonstrates improved balance between
reactivity and stability and coupling of haptens to proteins under
mild conditions with high incorporation efficiency
Linker-Doped Zeolitic Imidazolate Frameworks (ZIFs) and Their Ultrathin Membranes for Tunable Gas Separations
No full textZeolitic imidazolate
frameworks (ZIFs) have gained much interest
due to their potentials in gas separations. A hybrid approach by mixing
metals and/or linkers has been recently investigated to fine-tune
the ZIF framework porosity and surface properties and potentially
extending their separation applications for many important gas mixtures.
In general, the hybrid approach requires mixing of isostructural ZIFs
to maintain their topology, thus limiting the options of linkers and
metal centers to obtain hybrid ZIFs. Linker-doping, as reported here,
can be a strategy to expand the option of imidazolate linkers to obtain
mixed-linker hybrid ZIFs. Two linkers are investigated to be doped
into the ZIF-8 framework: 2-ethylimidazole (eIm) and 2-phenylimidazole
(phIm). The linker-doping strategy is shown to tune the “stiffness”
of Zn–N bonding as characterized by FT-IR, thereby the linker
flip-flopping motion of ZIF-8, which is analyzed through gas
adsorption isotherms. Furthermore, well-intergrown ultrathin eIm-doped
ZIF-8 membranes are grown on α-Al2O3 substrates,
in which the incorporation of eIm affects the morphology and thickness
of the polycrystalline membranes, improving the permeance of propylene
and propane molecules
Highly Deformable Nano-Cross-Linker-Bridged Nanocomposite Hydrogels for Water Management of Oil Recovery
No full textConventional
poly(acrylamide) (PAM)-based hydrogels suffered from
mechanical instability during water flooding, which markedly reduced
their performance for water management and oil recovery. In this report,
divinylbenzene (DVB) nanostructured cross-linker-bridged nanocomposite
hydrogels with high elasticity were described to increase hydrogel
mechanical integrity. Precipitation polymerization of DVB monomers
generated well-defined DVB nano-cross-linkers having styrenyl moieties
on the surfaces, as demonstrated by proton nuclear magnetic resonance
analysis. Frequency sweeps of the hydrogels confirmed the formation
of covalent junctions between PAM chains and DVB nano-cross-linkers
within the network. The nanocomposite hydrogels with covalent cross-links
showed a high degree of extensibility, greater than 40 times compared
to self-cross-linked N,N′-dimethylacrylamide
hydrogels with elongation of 14 and N,N′-methylenebis(acrylamide) cross-linked PAM hydrogel having
stretchability less than 2 times. The concentration of ammonium persulfate
initiator showed a greater effect on mechanical robustness than DVB
nano-cross-linkers. The increase in the initiator significantly increased
hydrogel extensibility upon stress. In addition, nano-cross-linker-based
hydrogel displayed slow swelling kinetics in brine in comparison to
commercially available LiquiBlock 40K gel. Low-cost DVB monomer-based
nano-cross-linker-bridged highly deformable hydrogels with excellent
elasticity rendered hydrogel production in industrial-scale feasible.
High deformation characteristics facilitated hydrogel propagation
through pore throats for in-depth fluid diversion
Degradable and Thermosensitive Microgels with Tannic Acid as the Sole Cross-Linker
No full textPoly(N-isopropylacrylamide) (PNIPAM)–tannic
acid (TA) microgels were successfully prepared via surfactant-free
emulsion polymerization (SFEP) at 70 °C in aqueous solution using N-isopropylacrylamide (NIPAM) as the monomer and a natural
polyphenol macromolecule, TA, as the sole cross-linker. The cross-linking
network of the PNIPAM–TA microgels was confirmed to contain
both physical cross-linking structures formed via hydrogen-bonding
interactions between TA and PNIPAM chains and chemical cross-linking
structures formed via capturing the radicals of propagating polymer
chains by catechol and pyrogallol groups of TA. Furthermore, TA was
applied to modify the surface of hydrophobic Fe3O4 nanoparticles, leading to hydrophilic Fe3O4@TA composite nanoparticles, which were successfully used as the
cross-linker to fabricate PNIPAM–Fe3O4@TA organic–inorganic hybrid microgels. The obtained PNIPAM–TA
and PNIPAM–Fe3O4@TA organic–inorganic
hybrid microgels had a uniform spherical shape with a relatively narrow
size distribution and exhibited thermosensitive behavior and pH-tunable
degradation. The PNIPAM–TA microgels were stable in the pH
range of 1.3–11.1 but underwent complete degradation with pH
above 11.4. The PNIPAM–Fe3O4@TA hybrid
microgels were partially degraded at pH values of 1.3 and 2.1, stable
in the pH range of 3.1–11.1, and underwent complete degradation
at pH above 11.4. The partial degradation of PNIPAM–Fe3O4@TA organic–inorganic hybrid microgels
under strong acidic conditions was attributed to the disintegration
of Fe3O4 nanoparticles. The complete degradation
of both microgels at pH above 11.4 was attributed to the hydrolysis
of ester groups of TA under strong alkali conditions
Crystallization of Galectin-8 Linker Reveals Intricate Relationship between the N-terminal Tail and the Linker
No full textGalectin-8 (Gal-8) plays a significant role in normal immunological function as well as in cancer. This lectin contains two carbohydrate recognition domains (CRD) connected by a peptide linker. The N-terminal CRD determines ligand binding specificity, whereas the linker has been proposed to regulate overall Gal-8 function, including multimerization and biological activity. Here, we crystallized the Gal-8 N-terminal CRD with the peptide linker using a crystallization condition that contains Ni2+. The Ni2+ ion was found to be complexed between two CRDs via crystal packing contacts. The coordination between Ni2+ and Asp25 plays an indirect role in determining the structure of β-strand F0 and in influencing the linker conformation which could not be defined due to its dynamic nature. The linker was also shortened in situ and crystallized under a different condition, leading to a higher resolution structure refined to 1.08 Å. This crystal structure allowed definition of a short portion of the linker interacting with the Gal-8 N-terminal tail via ionic interactions and hydrogen bonds. Observation of two Gal-8 N-terminal CRD structures implies that the N-terminal tail and the linker may influence each other’s conformation. In addition, under specific crystallization conditions, glycerol could replace lactose and was observed at the carbohydrate binding site. However, glycerol did not show inhibition activity in hemagglutination assay
ATP-dependent chromatosome remodeling
No full textChromatin serves to package, protect and organize the complex eukaryotic genomes to assure their stable inheritance over many cell generations. At the same time, chromatin must be dynamic to allow continued use of DNA during a cell's lifetime. One important principle that endows chromatin with flexibility involves ATP-dependent `remodeling' factors, which alter DNA-histone interactions to form, disrupt or move nucleosomes. Remodeling is well documented at the nucleosomal level, but little is known about the action of remodeling factors in a more physiological chromatin environment. Recent findings suggest that some remodeling machines can reorganize even folded chromatin fibers containing the linker histone H1, extending the potential scope of remodeling reactions to the bulk of euchromatin
Soft Mode Metal-Linker Dynamics in Carboxylate MOFs
No full text
Through comprehensive analysis of carboxylate-based metal-organic frameworks
(MOFs), we present general evidence for dynamic metal-linker bonding that challenges the
common perception of MOF structures being static. Structural dynamics in MOFs, however,
typically refers to the “breathing” behavior of pore cavities and the transient binding of guest
molecules, but dynamic bonding would explain important MOF phenomena in catalysis, post-
synthetic exchange, negative thermal expansion, and crystal growth. Here, we demonstrate through
use of variable-temperature diffuse reflectance infrared Fourier transform spectroscopy (VT-
DRIFTS) aided by ab initio plane wave density function theory, that similar evidence for melting
behavior in zeolitic imidazolate frameworks (ZIFs) can be observed for carboxylate MOFs by
monitoring the red-shifts of carboxylate stretches coupled to anharmonic metal-carboxylate
oscillators. To demonstrate the generality of these findings, we investigate a wide class of
carboxylate MOFs that includes iconic examples with diverse structures and metal-linker
chemistry. As the very vibrations invoked in ZIF melting, but heretofore unobserved for
carboxylate MOFs, these metal-linker dynamics resemble the ubiquitous soft modes that trigger
important phase transitions in diverse classes of materials, while offering a fundamentally new
perspective for the design of next-generation metal-organic materials.
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