Annual Reports on NMR Spectroscopy (eBook)

Graham A. Webb (Herausgeber)

eBook Download: PDF | EPUB

2011 | 1. Auflage
400 Seiten
Elsevier Science (Verlag)
978-0-08-056092-2 (ISBN)

Infos

Nuclear magnetic resonance (NMR) is an analytical tool used by chemists and physicists to study the structure and dynamics of molecules. In recent years, no other technique has grown to such importance as NMR spectroscopy. It is used in all branches of science when precise structural determination is required and when the nature of interactions and reactions in solution is being studied. Annual Reports on NMR Spectroscopy has established itself as a premier means for the specialist and nonspecialist alike to become familiar with new techniques and applications of NMR spectroscopy.

* Provides updates on the latest developments in NMR spectroscopy
* Includes comprehensive review articles
* Highlights the increasing importance of NMR spectroscopy as a technique for structural determination

Inhalt

Front cover 1
Annual Reports on NMR Spectroscopy 4
Copyright page 5
Contents 6
Contributors 8
Preface 10
Structure and Membrane Interactions of Antimicrobial Peptides as Viewed by Solid-State NMR Spectroscopy 12
1. Introduction 13
2. Study of Antimicrobial Peptides in Membranes 14
3. Effects of Antimicrobial Peptides on Model Lipid Membranes 26
4. Conclusions 30
References 30
Chemical Exchange 34
1. Introduction 34
2. Overview, Trends and Opinions 36
3. Theory 38
4. Methodology 43
5. Applications 46
6. Conclusions and Acknowledgments 54
References 55
Rhodium-103 NMR 60
1. Introduction 61
2. Acquisition of Data 62
3. Calibration of Spectra 63
4. Factors Underlying the Chemical Shift 65
5. Influence of Temperature on the Chemical Shift 68
6. Influence of Solvent on the Chemical Shift 69
7. Other Influences on the Chemical Shift 72
8. Correlation of d(103Rh) with Chemical and Structural Parameters 76
9. Parahydrogen-Induced Polarisation (PHIP) 87
10. High-Pressure Studies 89
11. Solid-State Studies 89
12. Clusters 91
13. Calculated Chemical Shifts 93
14. Spin Coupling Constants 95
15. Relaxation Times 98
16. Conclusion 99
Abbreviations 99
Acknowledgements 101
Appendix: Layout of Tables 101
References 178
The Indirect Detection of Metal Nuclei by Correlation Spectroscopy (HSQC and HMQC) 190
1. Introduction 191
2. 2D NMR Spectroscopy 197
3. Spin Systems 211
4. Review of Recent Reports of the Indirect Detection of Metal Nuclei 222
5. Conclusions 266
Abbreviations 266
Acknowledgements 268
References 268
Subject Index 274

Textauszug

Chapter 1

Structure and Membrane Interactions of Antimicrobial Peptides as Viewed by Solid-State NMR Spectroscopy

Marise Ouellet; Michèle Auger    Département de Chimie, CERSIM, CREFSIP, Université Laval, Québec, Québec, Canada, G1K 7P4

Abstract

Solid-state NMR spectroscopy is a well-suited technique to study the membrane interactions of antimicrobial peptides by taking advantage of the orientational dependence of nuclear spin interactions. This paper discusses several solid-state NMR experiments to extract information on the peptide structure and dynamics as well as on the effect of antimicrobial peptides on model membranes. More specifically, studies of peptide dynamics by 13C and 15N CP MAS and static experiments are reported. Also, the peptide orientation and location in membranes can be extracted from 15N 1D NMR spectra and spin diffusion NMR, whereas PISEMA experiments that correlate 15N chemical shifts and 15N–1H dipolar couplings allow the complete determination of membrane topology by specifying the peptide orientation and tilt angle. In addition, examples of peptide structure determination by isotropic chemical shifts, internuclear distance and torsion angle measurements are described. Finally, 31P NMR and 2H NMR experiments are commonly used to obtain information on both the polar region and the hydrophobic core of phospholipid bilayers. 31P NMR spectra reflect the nature of lipid phases and the conformation of the phospholipid polar headgroup, whereas 2H NMR spectra are indicative of acyl chain orientational order.

1 INTRODUCTION

The need to discover and develop novel antimicrobial compounds defeating the known mechanisms of bacterial resistance by the use of novel modes of action is becoming increasingly important due to the dramatic increase in bacterial resistance to numerous conventional antibiotics.1 In recent years, there has therefore been an increased popularity in the investigation of antimicrobial peptides that are found in several organisms and for which the structural and functional characteristics make them very promising therapeutic agents.2–7 Even though the exact mechanisms of action by which these antimicrobial peptides kill bacteria are still not completely understood, several studies have demonstrated that the interactions between antimicrobial peptides and the lipid membrane, leading to an increase in membrane permeability, play a major role in antimicrobial activity. In addition, because of these interactions, the antimicrobial peptides adopt a three-dimensional structure resulting in an amphipathic character.8–10 One of the most important factors that affects the activity of antimicrobial peptides appears to be the amphipathic character that is essential for the affinity of these peptidic units for the lipid bilayer.11–13 Several general mechanisms have been proposed in the literature in light of these studies to explain the membrane permeability caused by membrane-active peptides, and more specifically antimicrobial peptides. These general mechanisms, namely the “barrel-stave”, “carpet-like” and “toroidal” models, 14,15 are illustrated in Figure 1.

Figure 1 Cartoon illustrating membrane permeabilization mechanisms of antimicrobial peptides, namely the barrel-stave (left row), the carpet-like (middle row) and the toroidal (right row) models. The hydrophilic and hydrophobic faces of the peptide are coloured in black and grey, respectively. Top views are displayed for barrel and toroidal pores. Adapted from ref. 102 and reproduced with permissions.

One of the best suited techniques to investigate the structure and dynamics of peptides in interaction with anisotropic lipid membranes is solid-state nuclear magnetic resonance (NMR) spectroscopy.16–18 Several approaches have been developed to study these systems in which the restricted molecular motions leading to anisotropic nuclear spin interactions result in broad NMR spectra. An overview of the use of solid-state NMR spectroscopy to investigate both the structure and dynamics of antimicrobial peptides in interaction with membranes as well as the effects of antimicrobial peptides on membrane integrity are presented in this manuscript. Numerous techniques to investigate the structure, topology and dynamics of antimicrobial peptides in membranes will be presented in the first section while the second part will be devoted to the use of 31P and 2H solid-state NMR spectroscopy to study the effect of antimicrobial peptides on the hydrophilic and hydrophobic regions of lipid bilayers. Both sections will be supported by recent examples.

2 STUDY OF ANTIMICROBIAL PEPTIDES IN MEMBRANES

The structure and dynamics of peptides that are immobilized on the relevant NMR time scale17,19–21 can be investigated using solid-state NMR spectroscopy. Orientation-dependent shifts and splittings of the peptide resonances occur due to the anisotropic interactions that dominate solid-state NMR spectra. The study of NMR parameters such as the 15N and 13C chemical shifts and chemical shift anisotropy (CSA), and the dipolar couplings between 1H, 13C and 15N is therefore of great interest. This section will demonstrate how these parameters can be exploited to obtain information on the structure and dynamics of antimicrobial peptides in interaction with lipids.

2.1 Dynamics of antimicrobial peptides

The analysis of the spinning sideband intensity in magic-angle spinning (MAS) 13C or 15N spectra or of the CSA in static spectra can provide information about the dynamics of antimicrobial peptides incorporated into lipid membranes. The dynamics of the 18-residue antimicrobial peptide protegrin (PG-1) has been investigated by Buffy et al.22 using MAS spectra and this study has demonstrated that the dynamics differs depending on the lipid membrane composition. As shown in Figure 2, the intensity of the spinning sidebands in 13C NMR MAS spectra of the 13C labelled peptide is less important in dilauroylphosphatidylcholine (DLPC) bilayers compared to dimyristoylphosphatidylcholine (DMPC) and palmitoyloleoylphosphatidylcholine (POPC) bilayers, indicating a more rigid peptide in thicker lipid bilayers. The analysis of the 13Cα–Hα dipolar couplings for the Leu5 residue, which are 11.9 kHz in POPC and 2.0 kHz in DLPC, yielded similar results. The dynamics of PG-1 in DLPC bilayers was also investigated by Yamaguchi et al.23 using static 15N NMR spectroscopy. The decrease of the 15N CSA observed for PG-1 in lipid bilayers indicates increased motion compared to the static peptide. Buffy et al.24 have also performed similar studies with the cyclic antimicrobial peptide RTD-1 and the analysis of the spinning sidebands in 15N and 13C MAS spectra for the solid peptide and the peptide incorporated into DLPC bilayers demonstrated that the peptide is immobilized in bilayers.

Figure 2 13C CP-MAS spectra of the F12 13CO- and L5 13Cα-labelled Protegrin-1 peptide in DLPC (T=295 K) (top row), DMPC (T=313 K) (middle row) and POPC (T=295 K) (bottom row) bilayers with 2.5 kHz spinning. Best fits for the carbonyl spinning sideband patterns are shown below each experimental spectrum. Adapted from ref. 22 and reproduced with permissions.

2.2 Membrane orientation and topology of antimicrobial peptides

The membrane orientation of antimicrobial peptides can be determined using samples oriented with their normal parallel to the external magnetic field B0. These samples can be obtained by the mechanical alignment of the lipids between glass plates25 and the use of lanthanide-doped bicelles26 and these experiments are performed with peptides either selectively or uniformly labelled with 15N and/or 13C.

2.2.1 Membrane orientation from 1D spectra

The chemical shift obtained in samples oriented in the magnetic field B0 can be used to determine the membrane orientation of helicoidal antimicrobial peptides selectively 15N labelled at one position in the amino acid sequence. In particular, the σ33 element of the 15N CSA tensor is aligned along the NH bond for a α-helical peptide, and the NH bond vector is almost parallel to the helix axis. The peptide orientation can therefore be estimated by the analysis of the 15N chemical shift27 as illustrated in Figure 3. For peptides in β-sheet conformation, the situation is however more complex since the membrane orientation has to be determined from both the 13C and 15N chemical shifts of the carbonyl and amide groups, respectively. Since the majority of antimicrobial peptides present a helicoidal structure, these will be discussed in the present review. For more information about β-sheet peptides, the reader is referred to Buffy et al.24 and Yamaguchi et al.23

Figure 3 Membrane topology of a 15N labelled α-helical peptide in a lipid bilayer. The helical peptide in a transmembrane orientation gives chemical shift close to 200 ppm which corresponds to the downfield edge of the 15N powder pattern. A peptide flat on the bilayer surface gives a chemical shift close to 50 ppm which...

Produkt-Details

• Erscheint lt. Verlag: 6.9.2011
• Sprache: englisch
• Themenwelt: Sachbuch/Ratgeber
• Themenwelt: Naturwissenschaften ► Chemie ► Analytische Chemie
• Themenwelt: Naturwissenschaften ► Chemie ► Organische Chemie
• Themenwelt: Naturwissenschaften ► Chemie ► Physikalische Chemie
• Themenwelt: Naturwissenschaften ► Chemie ► Technische Chemie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie
• Themenwelt: Technik ► Bauwesen
• Themenwelt: Technik ► Umwelttechnik / Biotechnologie
• ISBN-10: 0-08-056092-X / 008056092X
• ISBN-13: 978-0-08-056092-2 / 9780080560922