Thermal stability and enzymatic activity of RNase A in the presence of cationic gemini surfactants

The thermal stability and enzymatic activity of bovine pancreatic ribonuclease A (RNase A) have been investigated in the presence of a homologous series of cationic gemini surfactants (alkanediyl-α,ω-bis(hydroxyethyl methyl hexadecyl ammonium bromide)). UV, circular dichorism and fluorescence spectroscopies have been used for this study. The denaturation curves at various surfactant concentrations were analyzed on basis of a two-transition model to obtain values of T m (temperature at the midpoint of denaturation) and ΔH m (enthalpy change at T m) of each transition. The main conclusion of this study is that these cationic gemini surfactants slightly activate and stabilize RNase A below their critical micelle concentrations at pH 5.0. The cationic gemini surfactant with the shorter spacer interacts more efficiently with RNase A than those with longer spacersPeer Reviewe

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

Gemini surfactants have two polar head groups and two hydrocarbon tails. Compared with conventional surfactants, geminis have much lower (οM vs. mM) critical micelle concentrations and possess slower (ms vs οs) monomer micelle kinetics. The structure of the gemini surfactants studied is [HOCH 2CH 2-, CH 3-, CH 3(CH 2) 15-N +-(CH 2) s-N +-(CH 2) 15CH 3,-CH 3,-CH 2CH 2OH]·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. © 2011 Elsevier Inc.Peer Reviewe