Interactions of gemini surfactants with two model proteins: NMR, CD, and fluorescence spectroscopies

• Published in: Journal of colloid and interface science 2012-03, Vol.369 (1), p.245-255
• Main Authors: Amiri, Razieh, Bordbar, Abdol-Khalegh, García-Mayoral, MaFlor, Khosropour, Ahmad Reza, Mohammadpoor-Baltork, Iraj, Menéndez, Margarita, Laurents, Douglas V.
• Format: Article
• Language: English
• Subjects: Animals; Chemistry; Chickens; Circular Dichroism; Circular dichroism spectroscopy; Colloidal state and disperse state; egg albumen; Exact sciences and technology; fluorescence; fluorescence emission spectroscopy; Fluorescence spectroscopy; Gemini surfactant; General and physical chemistry; Hen egg white lysozyme; hens; hydrogen; Hydrogen exchange; Isothermal titration calorimetry; lysozyme; Magnetic Resonance Spectroscopy; Membranes; micelles; Micelles. Thin films; Muramidase - chemistry; Muramidase - metabolism; nuclear magnetic resonance spectroscopy; Protein Conformation; Protein Denaturation; Ribonuclease A; Ribonuclease, Pancreatic - chemistry; Ribonuclease, Pancreatic - metabolism; ribonucleases; Spectrometry, Fluorescence; Surface-Active Agents - chemistry; Surface-Active Agents - metabolism; surfactants; Thermodynamics
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2011.11.062

[Display omitted] ► Cationic gemini surfactants do not interact with RNase A and HEWL at acidic pH. ► Hydrogen exchange NMR indicated that the stability of RNase A is lowered by about 1kcalmol−1. ► At alkaline pH, RNase A and HEWL do interact with gemini surfactants. ► Three different ProteinGemini complexes are formed including large aggregates. Gemini surfactants have two polar head groups and two hydrocarbon tails. Compared with conventional surfactants, geminis have much lower (μM vs. mM) critical micelle concentrations and possess slower (ms vs. μs) monomer ⇆ micelle kinetics. The structure of the gemini surfactants studied is [HOCH2CH2–, CH3–, CH3(CH2)15–N+–(CH2)s–N+–(CH2)15CH3,–CH3,–CH2CH2OH]·2Br− where s=4, 5, or 6. Our objective is to reveal the effect of these cationic gemini surfactants on the structure and stability of two model proteins: Ribonuclease A (RNase A) and Hen Egg White Lysozyme (HEWL). 2D 1H NMR and Circular Dichroism (CD) spectroscopies show that the conformation of RNase A and HEWL is unaffected at low to neutral pH where these proteins are positively charged, although hydrogen exchange shows that RNase A’s conformational stability is slightly lowered. At alkaline pH, where these proteins lose their net positive charge, fluorescence and CD spectroscopies and ITC experiments show that they do interact with gemini surfactants, and multiple protein•gemini complexes are observed. Based on the results, we conclude that these cationic gemini surfactants neither interact strongly with nor severely destabilize these well folded proteins in physiological conditions, and we advance that they can serve as useful membrane mimetics for studying the interactions between membrane components and positively charged proteins.