International Journal of Biological Macromolecules 58 (2013) 190–198 Contents lists available at SciVerse ScienceDirect International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac Surface behavior of -Synuclein and its interaction with phospholipids using the Langmuir monolayer technique: A comparison between monomeric and fibrillar -Synuclein Ali Chaari a,∗,1 , Habib Horchani b,1 , Fakher Frikha b , Robert Verger c , Youssef Gargouri b , Moncef Ladjimi a a Laboratoire de Génétique et Biologie Cellulaire Université de Versailles Saint Quentin en Yvelines, 45 avenue des Etats-Unis 78000, Versailles cedex, France b Laboratoire de Biochimie et de Génie Enzymatique des lipases, PB 1147, Sfax 3038, Tunisia c CNRS – Aix-Marseille Université – Enzymologie Interfaciale et Physiologie de la Lipolyse UMR 7282, 31 chemin Joseph Aiguier, 13402 Marseille cedex 20, France article info Article history: Received 10 February 2013 Received in revised form 12 March 2013 Accepted 23 March 2013 Available online 3 April 2013 Keywords: -Synuclein Monomer and fibrillar forms Monolayer technique abstract Due to the involvement of -Synuclein (-Syn) in lipid transport and its role in the normal function and in the pathology of Parkinson disease, it is important to study first the surface properties of the protein at the air/water interface and second its behavior related to biological membranes. For this purpose, the monomolecular film technique was used as membrane model to compare the interactions with various phospholipids of monomeric and fibrillar forms of -Syn. We have determined the equilibrium surface pressure of the two forms of -Syn (monomeric and fibrillar form) at the air/water interface. The surface pressures reached by monomeric -Syn were shown to be higher than the ones of fibrillar -Syn and similar to the value obtained by mellitin, a lytic peptide of bee venom, which has been described as “protein detergent”. The monomeric -Syn adsorbed more rapidly at the air/water interface with a maximal adsorption rate at least 60-times higher than the fibrillar form. In the presence of a phospholipid monolayer, the surface activities of two -Syn forms are much greater than observed at the air/water interface. Also we can show that the fibrillar form of -Syn have a higher value of critical pressure than the monomeric one for the cow brain extract and the Phospatidyl Glycerol (an anionic phospholipid) which confirm its higher affinity for the anionic phospholipid than the monomeric form. According these results, we can suggest that this aggregate form have important implications for the pathological activity and, therefore, for the associated neurotoxicity which can results in layer disruption and cell leakage. Published by Elsevier B.V. 1. Introduction -Synuclein (-Syn) belongs to a family of proteins including -, -, and -Synucleins that are encoded by three different genes [1–7] and is expressed at high levels in the brain and enriched in neural synaptic terminals. However, its physiological function remains largely unknown. Although, it has been suggested that -Syn plays a role in neuronal plasticity [6], development and in synaptogenesis [8]. Despite this, -Syn is only loosely associated Abbreviations: -Syn, alpha Synuclein; ThT, Thioflavine T; DLS, Dynamic Light Scat- tering; AFM, Atomic Force Microscopy; RH, Hydrodynamic Radius. ∗ Corresponding author. Present address: Weill Cornell Medical College in Qatar, Qatar Foundation – Education City, P.O. Box 24144, Doha, Qatar. Tel.: +974 4492 8432. E-mail addresses: ali.chaari@yahoo.fr, alc2033@qata-med.cornel.edu (A. Chaari). 1 Both authors should be considered as equal first author, and are listed in alpha- betical order. with either the synaptic membrane or synaptic vesicles, often behaving as a soluble protein in brain tissue extracts [6,9]. The human -Syn primary sequence is well conserved among vertebrates, with rodent and zebra fish -Syn being 95 and 87%, respectively, identical to the human sequence [1,4,6,10]. The amino-terminal sequence (residues 9–99) contains a series of amphipathic -helices that may facilitate membrane-protein and/or protein–protein interactions [11]. This region is composed of seven imperfect repeats of 11 amino acids, which contain a 6- residue core with the consensus sequence KTKEGV (Fig. 1) [11]. The central region of -Syn (residues 67–95) is very hydropho- bic (Fig. 1), and this internal fragment was initially isolated from Alzheimer’s disease senile plaques [9]. The C-terminal domain con- tains a sequence of acidic amino acids and three tyrosine residues, which are nitrated in Lewy body inclusions (Fig. 1) [12]. The C- terminal residues are believed to not participate in membrane binding, presumably being repelled by the negative surface charge of the lipid head groups [12]. There are no long-range tertiary 0141-8130/$ – see front matter. Published by Elsevier B.V. http://dx.doi.org/10.1016/j.ijbiomac.2013.03.057