Are stabilizing osmolytes preferentially excluded from the protein surface? FTIR and MD studies

Abstract

Interactions between osmolytes and hen egg white lysozyme in aqueous solutions were studied by means of FTIR spectroscopy and molecular dynamics. A combination of difference spectra method and chemometric analysis of spectroscopic data was used to determine the number of osmolyte molecules interacting with the protein, and the preferential interaction coefficient in presented systems. Both osmolytes -l-proline and trimethylamine-N-oxide (TMAO) - belong to a group of stabilizing osmolytes, and according to the preferential exclusion/hydration hypothesis, both should be excluded from the vicinity of the protein backbone and surface. We provide experimental and computational evidence that although TMAO behaves according to the hypothesis, proline does not. Our results suggest that preferential exclusion is not a universal property of stabilizing osmolytes.

Evidence for cooperative Na+ and Cl− binding by strongly hydrated l-proline

“…6 As a consequence, the hydration shell around the protein should be strengthened and thus its native conformation stabilized, suggesting that the protecting effect of Pro is indirect and mediated by the solvent. This contrasts the infrared study of Bruździak et al 7 who claim that Pro directly binds to proteins via its carboxylate group. With regard to freeze protection it is interesting to note that at very high Pro concentrations the solution does not freeze but exhibits a glass transition at 220 K 8 similar to water hydrating proteins.…”

“…It is still disputed whether Pro is excluded from the protein surface and thus enforces protein hydration 6 or selectively binds via its carboxylate group. 7 The present investigation cannot clarify this issue. However, if selective Pro binding to the protein occurs this has apparently no negative effect on protein stability.…”

“…Despite considerable efforts during the last decade to understand Pro-water interactions only a few publications describe its hydration structure. 6,7,[15][16][17][18][19][20][21][22][23][24][25] Moreover, the available quantitative information is scattered considerably. For instance, hydration numbers range from 20, obtained in a MD simulation, 15 to 11-12 from statistical mechanics 23 to 8-9, obtained with neutron diffraction.…”

Differential influence of additives on the various stages of insulin aggregation

“…55 The interaction of sucrose or ethylene glycol exists in the matured aggregates also, as a result of which the extent of aggregation decreases. In a recent study 56 it was found that the carboxyl groups are abundantly present on the surface of insulin brils.…”

Distinctive behavior and two-dimensional vibrational dynamics of water molecules inside glycine solvation shell

“…Small organic compounds or osmolytes such as the N-methylated glycine derivatives are produced in the living cells under unfavorable environmental conditions. [19][20][21] However, the mechanism of stabilization of the globular proteins by osmolytes [22][23][24] is still debatable 25 within the experimental and modeling approaches. [26][27][28][29][30] One hypothesis [31][32][33][34] demonstrates stabilization in terms of preferential exclusion of osmolytes from the protein surface, while the other considers solution structure and solvent properties to understand protein stability.…”