Is There a Preferential Interaction between Cholesterol and Tryptophan Residues in Membrane Proteins? †

Chemical Biology and Organic Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
Biochemistry (Impact Factor: 3.02). 03/2008; 47(8):2638-49. DOI: 10.1021/bi702235k
Source: PubMed


Recently, several indications have been found that suggest a preferential interaction between cholesterol and tryptophan residues located near the membrane-water interface. The aim of this study was to investigate by direct methods how tryptophan and cholesterol interact with each other and what the possible consequences are for membrane organization. For this purpose, we used cholesterol-containing model membranes of dimyristoylphosphatidylcholine (DMPC) in which a transmembrane model peptide with flanking tryptophans [acetyl-GWW(LA)8LWWA-amide], called WALP23, was incorporated to mimic interfacial tryptophans of membrane proteins. These model systems were studied with two complementary methods. (1) Steady-state and time-resolved Förster resonance energy transfer (FRET) experiments employing the fluorescent cholesterol analogue dehydroergosterol (DHE) in combination with a competition experiment with cholesterol were used to obtain information about the distribution of cholesterol in the bilayer in the presence of WALP23. The results were consistent with a random distribution of cholesterol which indicates that cholesterol and interfacial tryptophans are not preferentially located next to each other in these bilayer systems. (2) Solid-state 2H NMR experiments employing either deuterated cholesterol or indole ring-deuterated WALP23 peptides were performed to study the orientation and dynamics of both molecules. The results showed that the quadrupolar splittings of labeled cholesterol were not affected by an interaction with tryptophan-flanked peptides and, vice versa, that the quadrupolar splittings of labeled indole rings in WALP23 are not significantly influenced by addition of cholesterol to the bilayer. Therefore, both NMR and fluorescence spectroscopy results independently show that, at least in the model systems studied here, there is no evidence for a preferential interaction between cholesterol and tryptophans located at the bilayer interface.

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    • "As shown in Fig. 2 B, PI(4)P at 2 mol% 354, 373, and 393 nm (Fig. 1 B). These peaks are characteristic of DHE, which suggests fluorescence resonance energy transfer (FRET) from Osh4p to DHE (Schroeder et al., 1990; Holt et al., 2008; Liu et al., 2009). Osh4p contains several tryptophans close to the ergosterol-binding pocket, which should be responsible for the observed FRET signal (Fig. 1 C). "
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    The Journal of Cell Biology 12/2011; 195(6):965-78. DOI:10.1083/jcb.201104062 · 9.83 Impact Factor
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    • "), Demmers et al. (2001), Rinia et al. (2002), Strandberg et al. (2002), Petrache et al. (2002), Morein et al. (2002), van der Wel et al. (2002, 2007); Kol et al. (2003), Weiss et al. (2003), Andronesi et al. (2004), Ganchev et al. (2004), Strandberg et al. (2004), van Duyl et al. (2005), O ¨ zdirekcan et al. (2005, 2007), Im and Brooks (2005), Sparr et al. (2005a, b), Siegel et al. (2006), Holt et al. (2008) "
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    ABSTRACT: In this review we discuss recent insights obtained from well-characterized model systems into the factors that determine the orientation and tilt angles of transmembrane peptides in lipid bilayers. We will compare tilt angles of synthetic peptides with those of natural peptides and proteins, and we will discuss how tilt can be modulated by hydrophobic mismatch between the thickness of the bilayer and the length of the membrane spanning part of the peptide or protein. In particular, we will focus on results obtained on tryptophan-flanked model peptides (WALP peptides) as a case study to illustrate possible consequences of hydrophobic mismatch in molecular detail and to highlight the importance of peptide dynamics for the experimental determination of tilt angles. We will conclude with discussing some future prospects and challenges concerning the use of simple peptide/lipid model systems as a tool to understand membrane structure and function.
    Biophysics of Structure and Mechanism 12/2009; 39(4):609-21. DOI:10.1007/s00249-009-0567-1 · 2.22 Impact Factor
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    • "Recent examples of this kind include a study that demonstrated the absence of clustering of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P 2 ) in a fluid PC matrix at slightly above physiological pH, following the satisfactory description of FRET between 1,6- diphenylhexatriene (DPH) and NBD-labelled PI(4,5)P 2 , in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) vesicles with 5 mol% of total PI(4,5)P 2 (Fernandes et al. 2006) at pH 8.4. On the other hand, time-resolved FRET between the tryptophan residues of acetyl-GWW(LA) 8 LWWA-amide peptide (WALP23) and the fluorescent Chol analog dehydroergosterol (DHE), both with and without added equimolar amounts of Chol, could be satisfactorily globally analysed assuming uniform DHE distribution in the bilayer (Holt et al. 2008). This FRET pair (tryptophan/DHE) was also used in a study of the hypothetical affinity of the cM4 peptide from the muscle acetylcholine receptor (donor: Trp453) for Chol (acceptor: DHE) in the lo phase of POPC/Chol. "
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