Process Biochemistry 49 (2014) 623–630 Contents lists available at ScienceDirect Process Biochemistry jo ur nal home p age: www.elsevier.com/locate/procbio Molecular interaction of cationic gemini surfactant with bovine serum albumin: A spectroscopic and molecular docking study Muzaffar Ul Hassan Mir, Jitendra Kumar Maurya, Shahnawaz Ali, Shah Ubaid-ullah, Abbul Bashar Khan, Rajan Patel ∗ Biophysical Chemistry Laboratory, Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (A Central University), New Delhi, India a r t i c l e i n f o Article history: Received 27 July 2013 Received in revised form 23 December 2013 Accepted 18 January 2014 Available online 27 January 2014 Keywords: Bovine serum albumin Gemini surfactant Quenching Fluorescence Interaction Modelling a b s t r a c t Herein, we report the effect of N,N ′ -bis(dodecyloxycarbonylmethyl)-N,N,N ′ ,N ′ -tetramethyl-1,2- ethanediammonium dibromide (dodecyl betainate gemini or DBG) on the structure and function of bovine serum albumin (BSA) by using fluorescence, time resolved fluorescence, circular dichroism and dynamic light scattering techniques. The Stern–Volmer quenching constants K SV and the corresponding thermodynamic parameters viz H, G and S have been estimated by the fluorescence quenching method. The results indicated that DBG binds spontaneously with BSA through hydrophobic interaction. Time resolved fluorescence data show that the quenching follows the static mechanism pathway. It can be seen from far-UV CD spectra that the -helical network of BSA is disrupted and its content increases from 71% to 79% at lower concentrations which again decreases to 38% at higher concentration. DLS measurements suggested that hydrodynamic radius (R h ) decreases in the presence of 30 and 40 M of DBG while it increases when the concentration of DBG was 70 and 100 M. The molecular docking study indicated that DBG is embedded into subdomain IIA of BSA and binds with the R-914, R-195 and R-217 residues by hydrogen bonding and by hydrophobic interaction. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Protein exhibits dualism because of the hydrophobic and hydrophilic properties of the amino acids which causes pro- teins to interact with amphiphilic molecules. Due to the wide variety of applications like drug delivery, cosmetics and foods, protein–surfactant interactions have become a topic of consider- able interest [1,2]. Over a period of 50 years extensive studies have been done on protein–surfactant interactions [1]. Different types of physicochemical techniques have been employed to investigate the interactions between cationic and anionic surfactants with pro- teins in vitro [3–10]. The mechanism of such type of interactions has become an essential field of research in colloidal science [11–14]. The protein–surfactant interactions depend on many factors like charge on the head group, hydrophobic content and protein con- formation [15]. In addition, the binding of surfactants to protein alters the secondary structure of proteins which affects the func- tional properties of proteins. It may either enhance or reduce the protein stability depending on the nature of surfactants and sur- factant concentrations. Recent studies on protein–gemini systems ∗ Corresponding author. Tel.: +91 8860634100. E-mail addresses: rajanpatelpcy@gmail.com, rpatel@jmi.ac.in (R. Patel). show the alterations in the secondary structure of proteins [16–20]. Therefore, it is important to understand the protein–surfactant interactions at molecular level. New class of surfactants referred as the second generation sur- factants appeared recently in the scientific literature [21]. They bear two polar head groups and two non-polar aliphatic tails linked together covalently at or near the head groups by a third moiety called spacer, as schematically represented in Scheme 1. Such types of surfactants are known as gemini surfactants. Due to this peculiar architecture they have properties better than those possessed by their single chain counterparts like low critical micelle concentration (cmc), low kraft temperature, strong hydrophobic microdomain [21–24]. The low cmc values of gemini surfactants lowers the concentration of free non-micellized gemini surfac- tant molecules which in turn reduces the toxicity of the system and enhances the ability to dissolve the water insoluble materi- als. Due to this, their behaviour towards proteins is quiet different than conventional surfactants. Apart from better properties, they have better applications as well. They are used as additives in hair conditioners, antiseptics, skin and eye irritation-free cosmetics, shampoos, lotions, and personal care products [25,26]. Therefore, due to these interesting and useful applications of gemini surfactants, herein, we studied the effects of DBG on BSA. The molecular interactions between DBG and BSA were observed systematically by fluorescence, time resolved fluorescence, UV–vis 1359-5113/$ – see front matter © 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.procbio.2014.01.020