Journal
JOURNAL OF COLLOID AND INTERFACE SCIENCE
Volume 369, Issue -, Pages 245-255Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcis.2011.11.062
Keywords
Gemini surfactant; Ribonuclease A; Hen egg white lysozyme; Hydrogen exchange; Fluorescence spectroscopy; Circular dichroism spectroscopy; Isothermal titration calorimetry
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Funding
- Spanish Ministry of Science Innovation [CTQ 2010-21567-C02-02, BFU2009-10052]
- Research Council of the University of Isfahan
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Gemini surfactants have two polar head groups and two hydrocarbon tails. Compared with conventional surfactants, geminis have much lower (mu M vs. mM) critical micelle concentrations and possess slower (ms vs. mu s) monomer reversible arrow micelle kinetics. The structure of the gemini surfactants studied is [HOCH2CH2-, CH3-, CH3(CH2)(15)-N+-(CH2),-N+-(CH2)(15)CH3,-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 H-1 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 center dot 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. (C) 2011 Elsevier Inc. All rights reserved.
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