title: Effect of n-alkyl trimethylammonium bromides on folding and stability of alkaline and acid-denatured cytochrome c: a spectroscopic approach.
abstract: The molten globule (MG) state can be an intermediate in the protein folding pathway; thus, its detailed description can help understanding protein folding. Alkyl trimethylammonium bromides including dodecyl trimethylammonium bromide, DTAB; tetradecyl trimethylammonium bromide, TTAB; and hexadecyl trimethylammonium bromide, HTAB; cationic surfactants that are commonly used to mimic hydrophobic binding environments such as cell membranes, are known to denature some native state proteins, including horse cytochrome c (cyt c). In this article, refolding of alkaline and acid-denatured cyt c are studied under the influence of n-alkyl trimethylammonium bromides to form MG-like states at both low concentration (pH 11) and above the critical micelle concentration (pH 2) using ultraviolet and visible absorption, fluorescence and circular dichroism (CD). The addition of n-alkyl trimethylammonium bromides to the unfolded state of cyt c in alkaline and acidic condition appears to support the stabilized form of the MG state. The m-values of the refolded state of cyt c by DTAB, TTAB and HTAB showed substantial variation. The enhancement of m-values as the stability criterion of the MG state corresponded with increasing chain length of the cited n-alkyl trimethylammonium bromides. Based on the results obtained, the merits of two models of the protein-surfactant structure are discussed for various n-alkyl trimethylammonium bromides concentration in inducing the MG state at two different pH conditions. Therefore, hydrophobic interactions play a dominant role in stabilizing the MG state.
authors.affiliation: Department of Biology, Faculty of Science, Islamic Azad University-Mashhad Branch, Mashhad, Iran. chamani@ibb.ut.ac.ir
authors.forename: J
authors.initials: J
authors.lastname: Chamani
authors.forename: A A
authors.initials: AA
authors.lastname: Moosavi-Movahedi
mesh_terms: D000143:Acids; D000818:Animals; D001965:Bromides; D045304:Cytochromes c / Q000737:chemistry*; D006736:Horses; D057927:Hydrophobic and Hydrophilic Interactions; D011489:Protein Denaturation; D017510:Protein Folding; D013057:Spectrum Analysis; D013501:Surface-Active Agents
chemical_list: D000143:Acids; D001965:Bromides; D013501:Surface-Active Agents; D045304:Cytochromes c