Biomedical subjects

Sotirios Koutsopoulos

Publications and source records attributed to Sotirios Koutsopoulos.

6 recordsLinked to original sources

PubMed2006

Slow release of molecules in self-assembling peptide nanofiber scaffold.

Biological hydrogels consisting of self-assembling peptide nanofibers are potentially excellent materials for various controlled molecular release applications. The individual nanofiber consists of ionic self-complementary peptides with 16 amino acids (RADA16, Ac-RADARADARADARADA-CONH(2)) that are characterized by a stable beta-sheet structure and undergo self-assembly into hydrogels containing approximately 99.5% w/v water. We report here on the diffusion properties of phenol red, bromophenol blue, 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (pyranine, 3-PSA), 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (4-PSA), and Coomassie Brilliant Blue G-250 (CBBG) through RADA16 hydrogels. The apparent diffusivity (D ) of phenol red (1.05+/-0.08 x 10(-10) m(2) s(-1)) is higher than that of 3-PSA (0.050+/-0.004 x 10(-10) m(2) s(-1)) and 4-PSA (0.007+/-0.002 x 10(-10) m(2) s(-1)). The difference in 3-PSA and 4-PSA diffusivities suggests that the sulfonic acid groups directly facilitate electrostatic interactions with the RADA16 fiber surface. Bromophenol blue and CBBG were not released from the hydrogel, suggesting that they interact strongly with the peptide hydrogel scaffold. The diffusivities (D ) of the dyes decreased with increasing hydrogel peptide concentration, providing an alternate route of controlling release kinetics. These results indicate that release profiles can be tailored through controlling nanofiber-diffusant molecular level interactions.

Algorithms↗

PubMed2006

Thermal behavior of novel non-sonicated arsonolipid-containing liposomes.

The thermal properties of novel arsonolipid-containing liposomes in PBS pH 7.4 and in water in absence and presence of Ca(2+) ions are reported. Liposomes composed of arsonolipids with different acyl chains (C(12), C(16) and C(18)) were prepared by the one step method. Microcalorimetry results showed that (i) the thermotropic transitions of arsonoliposomes (in PBS, pH 7.4, and in water) increase as a function of arsonolipid fatty acyl chain length, (ii) arsonoliposomes of long fatty acyl chain arsonolipids (C(16) and C(18)) showed higher enthalpy and transition temperature in the buffer compared to those observed in water (for arsonoliposomes of C(12)-fatty acyl chain arsonolipid, the order was reversed which might be attributed to their different structure), and (iii) the presence of 2 mM CaCl(2) has more pronounced effects on the thermal properties of arsonoliposomes in distilled water than in buffer, which suggests that the ionic strength of the dispersion medium plays an important role in determining the thermal properties of arsonoliposomes.

Arsenicals↗

PubMed2005

Temperature-dependent structural and functional features of a hyperthermostable enzyme using elastic neutron scattering.

The dynamic behavior of an endoglucanase from the hyperthermophilic microorganism Pyrococcus furiosus was investigated using elastic neutron scattering. The temperature dependence of the atomic motions was correlated with conformational and functional characteristics of the enzyme. The onset of biological function at temperatures higher than approximately 25 degrees C (the hyperthermostable enzyme is essentially inactive at room temperature) was associated with a dynamical transition in the anharmonic motions domain. This transition from the nonactive to the enzymatically active conformation involved structurally similar conformational substates in the energy landscape. From the mean-square displacement of the protein atoms, the molecular flexibility and the effective force constants were calculated at different temperature zones. The results showed that the activity increases at higher temperatures where the intramolecular bonds are weakened and the overall rigidity of the protein is decreased. Further temperature increase resulted in significantly increased atomic fluctuations featuring heat denaturation of the protein.

Calorimetry↗

PubMed2005

Conformational studies of a hyperthermostable enzyme.

The structural features of the hyperthermophilic endo-beta-1,3-glucanase from Pyrococcus furiosus were studied using circular dichroism, steady-state and time-resolved fluorescence spectroscopy and anisotropy. Upon heat and chemical treatment the folded and denatured states of the protein were characterized by distinguishable spectral profiles that identified a number of conformational states. The fluorescence methods showed that the spectral differences arose from changes in the local environment around specific tryptophan residues in the native, partially folded, partially unfolded and completely unfolded state. A structural resemblance was observed between the native protein and the structurally perturbed state which resulted after heat treatment at 110 degrees C. The enzyme underwent disruption of the native secondary and tertiary structure only after incubation at biologically extremely high temperatures (i.e. 150 degrees C), whilst in the presence of 8 m of guanidine hydrochloride the protein was partially unfolded.

Anilino Naphthalenesulfonates↗

PubMed2004

Structural features of a hyperthermostable endo-beta-1,3-glucanase in solution and adsorbed on "invisible" particles.

Conformational characteristics and the adsorption behavior of endo-beta-1,3-glucanase from the hyperthermophilic microorganism Pyrococcus furiosus were studied by circular dichroism, steady-state and time-resolved fluorescence spectroscopy, and calorimetry in solution and in the adsorbed state. The adsorption isotherms were determined on two types of surfaces: hydrophobic Teflon and hydrophilic silica particles were specially designed so that they do not interact with light and therefore do not interfere with spectroscopic measurements. We present the most straightforward method to study structural features of adsorbed macromolecules in situ using common spectroscopic techniques. The enzyme was irreversibly adsorbed and immobilized in the adsorbed state even at high temperatures. Adsorption offered further stabilization to the heat-stable enzyme and in the case of adsorption on Teflon its denaturation temperature was measured at 133 degrees C, i.e., the highest experimentally determined for a protein. The maintenance of the active conformation and biological function particularly at high temperatures is important for applications in biocatalysis and biotechnology. With this study we also suggest that nature may employ adsorption as a complementary mode to maintain structural integrity of essential biomolecules at extreme conditions of temperature.

Adsorption↗

PubMedDate not supplied

In situ structure and activity studies of an enzyme adsorbed on spectroscopically undetectable particles.

The structural characteristics and the activity of a hyperthermophilic endoglucanase were investigated upon adsorption. Silica (hydrophilic) and Teflon (hydrophobic) surfaces were selected for the study. The materials were specially designed so that the interaction of the particles with light was negligible, and the enzyme conformation in the adsorbed state was monitored in situ. The adsorption isotherms were determined, and the adsorbed endoglucanase was studied using a number of spectroscopic techniques, enzymatic activity tests, and dynamic light scattering. Experiments were performed at pH values below, at, and above the isoelectric point of the enzyme. It was shown that the enzyme adsorbed on the hydrophobic surface of Teflon with higher affinity as compared to the hydrophilic silica nanoparticles. In all cases, adsorption was followed by (slight) changes in the secondary structure resulting in decreased beta-structural content. The changes were more profound upon adsorption on Teflon. The adsorbed enzyme remained active in the adsorbed state in spite of the structural changes induced when interacting with the surfaces.

Adsorption↗