Macromolecular crowding-induced molten globule states of the alkali pH-denatured proteins

Abstract

Structural and molecular properties extracted from circular dichroism (CD), tryptophan fluorescence and 1-anilino-8-napthalene sulfonate (ANS) binding experiments suggest that the high concentration of synthetic crowding agents (dextran 40, dextran 70 and ficoll 70) stabilizes and refolds the base-denatured ferricytochrome c (Ferricyt c) and lysozyme (Lyz) at pH 12.9 (±0.1) to molten globule (MG) states (C_B-states). These results further revealed that the C_B-states resemble the generic properties of MG-states. Thermodynamic analysis of thermal denaturation curves of base-denatured Ferricyt c and Lyz at pH 12.9 (±0.1) under variable concentrations of crowding agents (dextran 40, dextran 70 and ficoll 70) revealed that the crowder presence increases the thermal stability of base-denatured proteins and also prevents the cold denaturation of Ferricyt c. The results further showed that the nature, size and shape of crowder influence the crowding-mediated increase in secondary structure stabilization and thermal stability of base-denatured Ferricyt c and Lyz. Analysis of kinetic and thermodynamic parameters measured for CO association reaction of alkaline ferrocytochrome c (Ferrocyt c) at pH 12.9 (±0.1) under variable concentrations of crowding agents (dextran 40, dextran 70 and ficoll 70) revealed that the crowder presence reduces the level of structural fluctuation of M80-containing Ω-loop that control CO association to alkaline Ferrocyt c.

Keywords: Cold denaturation; Crowding agents; Enthalpy-entropy plot; Molten-globule state; Thermal stability.