| 1. |
- Del Giudice, Alessandra, et al.
(författare)
-
Structural response of human serum albumin to oxidation : Biological buffer to local formation of hypochlorite
- 2016
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 120:40, s. 12261-12271
-
Tidskriftsartikel (refereegranskat)abstract
- The most abundant plasma protein, human serum albumin (HSA), plays a key part in the body's antioxidant defense against reactive species. This study was aimed at correlating oxidant-induced chemical and structural effects on HSA. Despite the chemical modification induced by the oxidant hypochlorite, the native shape is preserved up to oxidant/HSA molar ratio <80, above which a structural transition occurs in the critical range 80-120. This conformational variation involves the drifting of one of the end-domains from the rest of the protein and corresponds to the loss of one-third of the α-helix and a net increase of the protein negative charge. The transition is highly reproducible suggesting that it represents a well-defined structural response typical of this multidomain protein. The ability to tolerate high levels of chemical modification in a folded or only partially unfolded state, as well as the stability to aggregation, provides albumin with optimal features as a biological buffer for the local formation of oxidants. (Graph Presented).
|
|
| 2. |
- Del Giudice, Alessandra, et al.
(författare)
-
The effect of fatty acid binding in the acid isomerizations of albumin investigated with a continuous acidification method
- 2018
-
Ingår i: Colloids and Surfaces B: Biointerfaces. - : Elsevier BV. - 0927-7765. ; 168, s. 109-116
-
Tidskriftsartikel (refereegranskat)abstract
- The protein Human Serum Albumin (HSA) is known to undergo conformational transitions towards partially unfolded forms triggered by acidification below pH 4.5. The extent of Fatty Acids (FA) binding has been thought to have an impact on the conformational equilibrium between the native and acid forms and to be a possible explanation for the observation of more than one band in early electrophoretic migration experiments at pH 4. We compared the acid-induced unfolding processes of commercial FA-free HSA, commercial “fatted” HSA and FA-HSA complexes, prepared at FA:HSA molar ratios between 1 and 6 by simple mixing and equilibration. We used a method for continuous acidification based on the hydrolysis of glucono-δ-lactone from pH 7 to pH 2.5, and followed the average protein changes by the blue shift of the intrinsic fluorescence emission and by performing a small angle X-ray scattering analysis on selected samples. The method also allowed for continuous monitoring of the increase of turbidity and laser light scattering of the protein samples related to the release of the insoluble ligands with acidification. Our results showed that the presence of FA interacting with albumin, an aspect often neglected in biophysical studies, affects the conformational response of the protein to acidification, and slightly shifts the loss of the native shape from pH 4.2 to pH 3.6. This effect increased with the FA:HSA molar ratio so that with three molar equivalents a saturation was reached, in agreement with the number of high-affinity binding sites reported for the FA. These findings confirm that a non-uniform level of ligand binding in an albumin sample can be an explanation for the early-observed conformational heterogeneity at pH 4.
|
|
| 3. |
- Del Giudice, Alessandra, et al.
(författare)
-
Time-Dependent pH Scanning of the Acid-Induced Unfolding of Human Serum Albumin Reveals Stabilization of the Native Form by Palmitic Acid Binding
- 2017
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 121:17, s. 4388-4399
-
Tidskriftsartikel (refereegranskat)abstract
- The most abundant plasma protein, human serum albumin (HSA), is known to undergo several conformational transitions in an acidic environment. To avoid buffer effects and correlate global and local structural changes, we developed a continuous acidification method and simultaneously monitored the protein changes by both small-angle scattering (SAXS) and fluorescence. The progressive acidification, based on the hydrolysis of glucono-δ-lactone from pH 7 to pH 2.5, highlighted a multistep unfolding involving the putative F form (pH 4) and an extended and flexible conformation (pH < 3.5). The scattering profile of the F form was extracted by component analysis and further 3D modeled. The effect of acid unfolding at this intermediate stage was assigned to the rearrangement of the three albumin domains drifting apart toward a more elongated conformation, with a partial unfolding of one of the outer domains. To test the stabilizing effect of fatty acids, here palmitic acid, we compared the acid unfolding process of albumin with and without ligand. We found that when binding the ligand, the native conformation was favored up to lower pH values. Our approach solved the problem of realizing a continuous, homogeneous, and tunable acidification with simultaneous characterization applicable to study processes triggered by a pH decrease.
|
|
| 4. |
- di Gregorio, Maria Chiara, et al.
(författare)
-
pH Sensitive Tubules of a Bile Acid Derivative: a Tubule Opening by Release of Wall Leaves
- 2013
-
Ingår i: Physical Chemistry Chemical Physics. - 1463-9084. ; 15:20, s. 7560-7566
-
Tidskriftsartikel (refereegranskat)abstract
- Tubules formed by self-assembly of organic molecules have a vast potential in nanotechnology applications and the introduction of sensitivity to stimuli into self-assembly tubules represents a particularly attractive feature. Here we report on the preparation and characterization of a molecule obtained by chemical modification of a natural bile acid, a biological surfactant, that self-assembles in pH sensitive tubules in aqueous solutions. The tubules, that are rigid, single-walled and with a diameter of 60 nm, form at pH 8-9 and open up when the pH is increased. The transition is reversible, it occurs in the pH range of 9-10 with an opening mechanism that is remarkably different from those so far proposed in the literature. It involves a release of wall layers similar to leaves, and is determined by a drastic pH-triggered change in the molecular arrangement, which in turn induces a radical modification of the wall curvature. The description of the morphological transformation is performed by means of cryogenic transmission electron microscopy and represent, to our knowledge, the first detailed visualization of pH stimulated tubule opening. UV and circular dichroism spectroscopies are used to investigate the evolution at the molecular level.
|
|
| 5. |
- Du, Guanqun, et al.
(författare)
-
Effect of temperature on the association behavior in aqueous mixtures of an oppositely charged amphiphilic block copolymer and bile salt
- 2020
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 206
-
Tidskriftsartikel (refereegranskat)abstract
- The association in aqueous mixtures of a thermoresponsive cationic diblock copolymer composed of poly(N-isopropylacrylamide) (PNIPAM) and poly(3-acrylamidopropyl)-trimethylammonium-chloride (PAMPTMA(+)) and the oppositely charged bile salt sodium deoxycholate (NaDC) is investigated at different compositions by light and X-ray scattering, calorimetry, and electrophoretic mobility measurements. Clouding reveals aggregation upon heating. The addition of NaDC to the copolymer solution lowers the temperature of the transition and increases its cooperativity. At high temperature and low NaDC fractions, mixed aggregates with a dehydrated PNIPAM-rich interior and a PAMPTMA(+)-rich shell partially neutralized by DC– anions are formed. At high NaDC fractions, the aggregates present internal regularly spaced segregated nanoregions of dehydrated PNIPAM and PAMPTMA(+)/DC– (microphase separation). The results suggest that the mixed aggregates have appealing composition-controlled thermoresponse. The system phase separates at body temperature and the highest NaDC fractions investigated, meaning in conditions accomplished when the use of the polymer as a bile salt sequestrant is hypothesized.
|
|
| 6. |
- Gubitosi, M., et al.
(författare)
-
On the stability of lithocholate derivative supramolecular tubules
- 2017
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 7:1, s. 512-517
-
Tidskriftsartikel (refereegranskat)abstract
- The self-assembly of a mannose-labelled bile salt derivative gives rise to a metastable nematic phase of monodisperse nanotubes in aqueous solutions that are characterized by a crystalline order. This work is addressed to study the relative stability of these tubular aggregates in order to have full control of such a system for possible applications. By using a static light scattering method we evaluate both the solubilities of the metastable nanotubes and of stable nanocrystals, demonstrating that these are remarkably lower than the critical micellar concentration of typical bile salts and other ionic conventional surfactants. A partial stability map is developed by combining solubility and calorimetry data, where a nematic nanotube phase region is highlighted below 60-65 °C.
|
|
| 7. |
- Gubitosi, Marta, et al.
(författare)
-
Sugar-Bile Acid-Based Bolaamphiphiles: From Scrolls to Monodisperse Single-Walled Tubules.
- 2014
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:22, s. 6358-6366
-
Tidskriftsartikel (refereegranskat)abstract
- The introduction of a mannose residue on carbon 3 of lithocholic acid gives rise to an asymmetric and rigid bolaamphiphilic molecule, which self-assembles in water to form elongated tubular aggregates with an outer diameter of about 20 nm. These tubular structures display a temporal evolution, where the average tube diameter decreases with time, which can be followed by time-resolved small-angle X-ray scattering experiments. Cryogenic transmission electron microscopy images collected as a function of time show that at short times after preparation tubular scrolls are formed via the rolling of layers, after which a complex transformation of the scrolls into single-walled tubules takes place. At long time scales, a further evolution occurs where the tubules both elongate and become narrower. The observed self-assembly confirms the tendency of bile acids and their derivatives to form supramolecular aggregates with an ordered packing of the constituent molecules. It also demonstrates that scrolls can be formed as intermediate structures in the self-assembly process of monodisperse single-walled tubules.
|
|
| 8. |
- Gubitosi, Marta, et al.
(författare)
-
Tailoring Supramolecular Nanotubes by Bile Salt Based Surfactant Mixtures.
- 2015
-
Ingår i: Angewandte Chemie (International edition). - : Wiley. - 1521-3773. ; 54:24, s. 7018-7021
-
Tidskriftsartikel (refereegranskat)abstract
- An approach for tailoring self-assembled tubular structures is described. By controlling the relative composition of a two-component surfactant mixture comprising the natural bile salt lithocholate and its bolamphiphilic derivative, it was possible to finely tune the nanotube cross-section of the mixed tubular aggregates that self-associated spontaneously in aqueous solution at pH 12. The diameter was found to vary up to 50 % when the stoichiometric ratio of the two bile salts was changed. The tuning of supramolecular nanochannels with such remarkable precision is of significant interest for technological applications of these materials.
|
|
| 9. |
- Janiak, John, et al.
(författare)
-
Nanoparticles with a Bicontinuous Cubic Internal Structure Formed by Cationic and Non-ionic Surfactants and an Anionic Polyelectrolyte.
- 2012
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:48, s. 16536-16546
-
Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles with an internal structure have been prepared by dispersing under dilute conditions poly(acrylic acid) with a polymerization degree n = 6000 (PAA6000) together with a cationic surfactant hexadecyltrimethylammonium hydroxide (C16TAOH) and the non-ionic surfactant penta(ethylene glycol) monododecyl ether (C12E5) in water. The nanoparticles are formed at different mixing ratios in the corresponding two-phase regions (liquid crystalline phase/dilute isotropic phase) of the C16TAPA6000 complex salt/ C12E5/water ternary phase diagram. The particles consist of polyacrylate PA6000 − polyions, C16TA+ surfactant ions, and C12E5. Their internal ordering was identified by small-angle Xray scattering (SAXS) to be either bicontinuous cubic with the Ia3d crystallographic space group or normal hexagonal depending upon the amount of C12E5. The bicontinuous cubic phase, to our knowledge never observed before in polyelectrolyte−surfactant particle systems, was inferred by SAXS experiments. The data also showed that this structure is thermoresponsive in a reversible manner. The bicontinuous cubic space group transforms from Ia3d to Im3m as the temperature decreases from 25 to 15 °C. According to dynamic light scattering and electrophoretic mobility measurements, the particles have a well-defined size (apparent hydrodynamic radii RH in the range of 88−140 nm) and carry a positive net charge. The size of the nanoparticles is stable up to 1 month. The faceted nanoparticles are visualized by cryogenic transmission electron microscopy that also reveals their coexistence with thread-like C12E5 micelles.
|
|
| 10. |
- Schillén, Karin, et al.
(författare)
-
Block copolymers as bile salt sequestrants : Intriguing structures formed in a mixture of an oppositely charged amphiphilic block copolymer and bile salt
- 2019
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 21:23, s. 12518-12529
-
Tidskriftsartikel (refereegranskat)abstract
- To study the formation and characterize the structure of mixed complexes of oppositely charged block copolymers and surfactants are of great significance for practical applications, e.g., in drug carrier formulations that are based on electrostatically assisted assembly. In this context, biocompatible block copolymers and biosurfactants (like bile salts) are particularly interesting. In this work, we report on the co-assembly in dilute aqueous solution between a cationic poly(N-isopropyl acryl amide) (PNIPAM) diblock copolymer and the oppositely charged bile salt surfactant sodium deoxycholate at ambient temperature. The cryogenic transmission electron microscopy (cryo-TEM) experiments revealed the co-existence of two types of co-assembled complexes of radically different morphology and inner structure. They are formed mainly as a result of the electrostatic attraction between the positively charged copolymer blocks and bile salt anions and highlight the potential of using linear amphiphilic block copolymers as bile salt sequestrants in the treatment of bile acid malabsorption and hypercholesterolemia. The first complex of globular morphology has a coacervate core of deoxycholate anions and charged copolymer blocks surrounded by a PNIPAM corona. The second complex has an intriguing tape-like supramolecular morphology of several micrometer in length that is striped in the direction of the long axis. A model is presented in which the stretched cationic blocks of several block copolymers interact electrostatically with the bile salt molecules that are associated to form a zipper-like structure. The tape is covered on both sides by the PNIPAM chains that stabilize the overall complex in solution. In addition to cryo-TEM, the mixed system was investigated in a range of molar charge fractions at a constant copolymer concentration by static light scattering, small angle X-ray scattering, and electrophoretic mobility measurements.
|
|
