Short Communication Conformational dynamics of a hydrophobic prion fragment (113–127) in different pH and osmolyte solutions Mohammed Inayathullah a,b,c , Jayakumar Rajadas a,c, ⁎ a Biomaterials and Advanced Drug Delivery Laboratory, School of Medicine, Stanford University, Palo Alto, CA 94304, USA b Bioorganic and Neurochemistry Laboratory, Central Leather Research Institute, Adyar, Chennai, Tamil Nadu 600020, India c Cardiovascular Pharmacology Division, Cardiovascular Institute, School of Medicine, Stanford University, Stanford, CA 94305, USA abstract article info Article history: Received 22 November 2015 Received in revised form 9 February 2016 Accepted 14 February 2016 Available online xxxx Prion diseases are characterized by a conformational change in prion protein from its native state into beta-sheet rich aggregates that are neurotoxic. The central domain that contain a highly conserved hydrophobic region of the protein play an important role in the toxicity. The conformation of the proteins is largely influenced by var- ious solvent environments. Here we report results of study of hydrophobic prion fragment peptide PrP(113–127) under different pH and osmolytes solution conditions. The secondary structure and the folding of PrP(113–127) was determined using circular dichroism and fluorescence spectroscopic methods. The results indicate that PrP(113–127) adopts a random coil conformation in aqueous buffer at neutral pH and that converted into beta sheet on aging. Even though the initial random coil conformation was similar in different pH conditions, the acidic as well as basic pH conditions delays the conformational transition to beta sheet. FRET results indicate that the distance between N and C-terminal regions increased on aging due to unfolding by self-assembly of the peptide into an organized beta sheet structure. Presence of osmolytes, prevented or decelerated the aggregation process of PrP(113–127) peptide. © 2016 Published by Elsevier Ltd. Keywords: Amyloid Prion Peptide Self-assembly Conformation Circular dichroism FRET Osmolytes 1. Introduction Conformational changes in the prion protein are the fundamental event involved in the development of prion related encephalopathies (Haldiman et al., 2013). The defining features of these diseases are the misfolding of innocuous cellular prion protein (PrP C ) into a neurotoxic and infectious isoform (PrP Sc )(Prusiner, 1998). The central domain of PrP C (residues 95–133) comprises two regions, the charged cluster (95–110) and the hydrophobic core (112–133) that are associated in the neurotoxicity (Vilches et al., 2013). The major conformational changes occur in the C-terminal globular domain of PrP, and the pertur- bation of which has been shown to result in the transition to PrP Sc by mechanistic and computational studies (Menon and Sengupta, 2015; Wu et al., 2015; Ziegler et al., 2003). However, it has been shown that deletion of a segment of PrP that overlaps the hydrophobic core produced a PrP that does not convert to PrP Sc (Holscher et al., 1998; Muramoto et al., 1996). Though the mechanisms that facilitate the conformational change remain unclear (Kupfer et al., 2009; Surewicz and Apostol, 2011), it appears that the hydrophobic region is directly involved in this process (Brown, 2000; Norstrom and Mastrianni, 2005), and that the conservation of this region is essential for infectivity (Harrison et al., 2010). Prp(106–126) of human prion protein, which corresponds to a highly conserved region of PrP, located in the N- terminal segment adjacent to the structurally organized globular domain (Donne et al., 1997). Several researchers have used a synthetic PrP C fragment of 21 residues of the central domain PrP(106–126) as a model of prion neurotoxicity (Forloni et al., 1993; Walsh et al., 2010). PrP(106–126) contains a polar head (KTNMKHM), PrP(106–112) at N- terminal followed by a long hydrophobic tail (AGAAAAGAVVGGLG), PrP(113–126) that contain the palindromic sequence AGAAAAGA, also been shown to be crucial for the propagation of prion toxicity (Norstrom and Mastrianni, 2005; Zhang and Zhang, 2013). PrP(113–127), a pentadecapeptide is known as fibrillogenic se- quence of Prion peptide consists of an alanine rich hydrophobic region (Gasset et al., 1992; Inayathullah et al., 2013; Satheeshkumar and Jayakumar, 2003). The secondary structure this hydrophobic fragment significantly influenced by several physiological factors such as ionic- strength, pH, solvent composition, and other factors (De Gioia et al., 1994; Inayathullah et al., 2013; Satheeshkumar and Jayakumar, 2003), whereas the polar head region has been reported to have least effect at different pH and other solvent environments (Di Natale et al., 2005). Whenever protein experiences stress due to any change in envi- ronmental conditions (extreme pH, high temperature, pressure etc.) most cells utilize small organic solutes (osmolytes) to protect proteins from denaturing. Osmolytes such as glycerol, trimethylamine N-oxide (TMAO), etc., are known to stabilize native conformation of prion and Neuropeptides xxx (2016) xxx–xxx ⁎ Corresponding author at: Stanford University, 1050 Arastradero Road, Room A148, Palo Alto, CA 94304, USA. E-mail address: jayraja@stanford.edu (J. Rajadas). YNPEP-01711; No of Pages 6 http://dx.doi.org/10.1016/j.npep.2016.02.004 0143-4179/© 2016 Published by Elsevier Ltd. Contents lists available at ScienceDirect Neuropeptides journal homepage: www.elsevier.com/locate/npep Please cite this article as: Inayathullah, M., Rajadas, J., Conformational dynamics of a hydrophobic prion fragment (113–127) in different pH and osmolyte solutions, Neuropeptides (2016), http://dx.doi.org/10.1016/j.npep.2016.02.004