Biomolecular interactions of lysosomotropic surfactants with cytochrome c and its effect on the protein conformation: A biophysical approach Tomasz Janek a, ⁎, Przemysław Czeleń b , Eduardo J. Gudiña c , Lígia R. Rodrigues c , Żaneta Czyżnikowska d a Department of Biotechnology and Food Microbiology, Wroclaw University of Environmental and Life Sciences, 51-630 Wroclaw, Poland b Department of Physical Chemistry, Faculty of Pharmacy, Collegium Medium, Nicolaus Copernicus University, 85-950 Bydgoszcz, Poland c Centre of Biological Engineering, University of Minho, 4710-057 Braga, Portugal d Department of Inorganic Chemistry, Faculty of Pharmacy, Wroclaw Medical University, 50-556 Wroclaw, Poland abstract article info Article history: Received 27 November 2018 Received in revised form 19 December 2018 Accepted 5 January 2019 Available online 06 January 2019 The molecular interactions between two single-chain lysosomotropic surfactants DMM-11 (2-Dodecanoyloxyethyl) trimethylammonium bromide) and DMPM-11 (2-Dodecanoyloxypropyl)trimethylammonium bromide) with a small heme-protein (cytochrome c (cyt-c)) in Hepes buffer (pH = 7.4) were extensively investigated by surface ten- sion, dynamic light scattering (DLS), circular dichroism (CD) and fluorescence spectroscopy in combination with molecular dynamic simulation techniques. The results demonstrated that surfactants can destroy the hydrophobic cavity of cyt-c, make the α-helical become loose and convert it into the β-sheet structure. The interactions between surfactants and cyt-c are mainly hydrophobic. Molecular modelling approaches were also used to gather a deeper insight on the binding of lysosomotropic surfactants with cyt-c and the in silico results were found to be in good agreement with the experimental ones. This study provides a molecular basis for the applications of protein- surfactant complexes in biological, food, pharmaceutical, industrial and cosmetic systems. © 2019 Elsevier B.V. All rights reserved. Keywords: Lysosomotropic surfactant Cytochrome c Fluorescence quenching Circular dichroism Molecular dynamic simulations 1. Introduction Interactions between proteins and surfactants have been studied for many years [1–6], not only due to their fascinating structural organiza- tion, but also to their potential technological applications in biosciences, drug delivery, medicine and food industry. The surfactant-protein com- plexes become more hydrophilic than either the surfactant or the pro- tein themselves, and the effective increase of the complexes solubility avoids the formation of higher order aggregates [7]. Mostly, electrostatic interactions and hydrophobic associations are the two main driving forces that contribute for the surfactant-protein interactions [8,9]. Like- wise, surfactants can cause protein conformational changes leading to the protein folding or unfolding depending on the concentrations of both surfactants and proteins. Several biophysical methods such as iso- thermal titration calorimetry [4], surface tension analysis [10], fluores- cence [11] and circular dichroism spectroscopy [12] have been used to unravel the interactions between surfactants and proteins. Parray et al. [13] reported the interactions between cationic gemini surfactant and its monomeric counterpart with phospholipase A 2 , and the results indicated that the tuning of the protein conformations by surfactants changes according to the structure of the surfactants used. Janek et al. [4] studied the interactions between bovine serum albumin (BSA) and cationic quaternary ammonium surfactants (QACs) using the synchro- nous fluorescence method, and the experiments showed that surfac- tants mainly interacted with the tryptophan residues of BSA. Hu et al. [14] estimated the Stern–Volmer quenching constants K SV and the cor- responding thermodynamic parameters ΔH, ΔG and ΔS of the interac- tions between BSA and surfactants by the fluorescence quenching method. It was noted that the hydrophobic forces are the predominant intermolecular forces between BSA and the surfactant. An interesting group of lysosomotropic surfactants are the cationic QACs which, according to their amphiphilic nature, can partition to the phospholipid bilayer and translocate across membranes as un- charged molecules [6]. In contrast to other surfactants that kill cells by acting at the plasma membrane, lysosomotropic surfactants primarily act on within the lysosomes [15]. Several soft cationic QACs showed bi- ological activities against several pathogenic bacterial strains [16], fila- mentous fungi [17] and also some human tumor cell lines [18]. Therefore, soft cationic QACs can potentially be used in lysosome- targeting anti-cancer drugs [19–21]. Cationic QACs can enter the lyso- some and possibly induce conformational changes of the proteins in- volved in apoptosis [22]. In our experiments we used cytochrome c (cyt-c) as a model protein for various interactions. Cyt-c is a kind of iron-containing metalloprotein International Journal of Biological Macromolecules 126 (2019) 1177–1185 ⁎ Corresponding author at: Department of Biotechnology and Food Microbiology, Wrocław University of Environmental and Life Sciences, 51-630 Wrocław, Poland E-mail address: tomasz.janek@upwr.edu.pl (T. Janek). https://doi.org/10.1016/j.ijbiomac.2019.01.024 0141-8130/© 2019 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect International Journal of Biological Macromolecules journal homepage: http://www.elsevier.com/locate/ijbiomac