Protein-polysaccharide viscoelastic matrices: synergic effects of amylose on lysozyme physical gelation in aqueous dimethylsulfoxide

A synergic effect of amylose on rheological characteristics of lysozyme physical gels evolved out of dimethylsulfoxide-water was verified and analyzed. The dynamics of the gels were experimentally approached by oscillatory rheology. The synergic effect was characterized by a decrease in the threshold DMSO volume fraction required for lysozyme gelation, and by a significant strengthening of the gel structure at over-critical solvent and protein concentrations. Drastic changes in the relaxation and creep curve patterns for systems in the presence of amylose were verified. Complex viscosity dependence on temperature was found to conform to an Arrhenius-like equation, allowing the determination of an activation energy term (Ea, apparent) for discrimination of gel rigidity. A dilatant effect was found to be induced by temperature on the flow behavior of lysozyme dispersions in DMSO-H(2)O in sub-critical conditions for gelation, which was greatly intensified by the presence of amylose in the samples. That transition was interpreted as reflecting a change from a predominant colloidal flow regime, where globular components are the prevailing structural elements, to a mainly fibrillar, polymeric flow behavior.FAPESP (Brazil

DMSO-induced denaturation of hen egg white lysozyme

\u3cp\u3eWe report on the size, shape, structure, and interactions of lysozyme in the ternary system lysozyme/DMSO/water at low protein concentrations. Three structural regimes have been identified, which we term the folded (0 < \u3csub\u3eDMSO\u3c/sub\u3e < 0.7), unfolded (0.7 ≤ \u3csub\u3eDMSO\u3c/sub\u3e < 0.9), and partially collapsed (0.9 ≤ \u3csub\u3eDMSO\u3c/sub\u3e < 1.0) regime. Lysozyme resides in a folded conformation with an average radius of gyration of 1.3 ± 0.1 nm for \u3csub\u3eDMSO\u3c/sub\u3e < 0.7 and unfolds (average R\u3csub\u3eg\u3c/sub\u3e of 2.4 ± 0.1 nm) above \u3csub\u3eDMSO\u3c/sub\u3e > 0.7. This drastic change in the protein's size coincides with a loss of the characteristic tertiary structure. It is preceded by a compaction of the local environment of the tryptophan residues and accompanied by a large increase in the protein's overall flexibility. In terms of secondary structure, there is a gradual loss of α-helix and concomitant increase of β-sheet structural elements toward \u3csub\u3eDMSO\u3c/sub\u3e = 0.7, while an increase in \u3csub\u3eDMSO\u3c/sub\u3e at even higher DMSO volume fractions reduces the presence of both α-helix and β-sheet secondary structural elements. Protein-protein interactions remain overall repulsive for all values of \u3csub\u3eDMSO\u3c/sub\u3e. An attempt is made to relate these structural changes to the three most important physical mechanisms that underlie them: the DMSO/water microstructure is strongly dependent on the DMSO volume fraction, DMSO acts as a strong H-bond acceptor, and DMSO is a bad solvent for the protein backbone and a number of relatively polar side groups, but a good solvent for relatively apolar side groups, such as tryptophan.\u3c/p\u3

DMSO-induced denaturation of hen egg white lysozyme

We report on the size, shape, structure, and interactions of lysozyme in the ternary system lysozyme/DMSO/water at low protein concentrations. Three structural regimes have been identified, which we term the “folded” (0 DMSO DMSO DMSO DMSO Rg of 2.4 ± 0.1 nm) above φDMSO > 0.7. This drastic change in the protein’s size coincides with a loss of the characteristic tertiary structure. It is preceded by a compaction of the local environment of the tryptophan residues and accompanied by a large increase in the protein’s overall flexibility. In terms of secondary structure, there is a gradual loss of α-helix and concomitant increase of β-sheet structural elements toward φDMSO = 0.7, while an increase in φDMSO at even higher DMSO volume fractions reduces the presence of both α-helix and β-sheet secondary structural elements. Protein−protein interactions remain overall repulsive for all values of φDMSO. An attempt is made to relate these structural changes to the three most important physical mechanisms that underlie them: the DMSO/water microstructure is strongly dependent on the DMSO volume fraction, DMSO acts as a strong H-bond acceptor, and DMSO is a bad solvent for the protein backbone and a number of relatively polar side groups, but a good solvent for relatively apolar side groups, such as tryptophan