Abstract
Many naturally occurring bioactive peptides bind to biological membranes. Studying and elucidating the mode of interaction is often an essential step to understand their molecular and biological functions. To obtain the complete orientation and immersion depth of such compounds in the membrane or a membrane-mimetic system, a number of methods are available, which are separated in this review into four main classes: solution NMR, solid-state NMR, EPR and other methods. Solution NMR methods include the Nuclear Overhauser Effect (NOE) between peptide and membrane signals, residual dipolar couplings and the use of paramagnetic probes, either within the membrane-mimetic or in the solvent. The vast array of solid state NMR methods to study membrane-bound peptide orientation and localization includes the anisotropic chemical shift, PISA wheels, dipolar waves, the GALA, MAOS and REDOR methods and again the use of paramagnetic additives on relaxation rates. Paramagnetic additives, with their effect on spectral linewidths, have also been used in EPR spectroscopy. Additionally, the orientation of a peptide within a membrane can be obtained by the anisotropic hyperfine tensor of a rigidly attached nitroxide label. Besides these magnetic resonance techniques a series of other methods to probe the orientation of peptides in membranes has been developed, consisting of fluorescence-, infrared- and oriented circular dichroism spectroscopy, colorimetry, interface-sensitive X-ray and neutron scattering and Quartz crystal microbalance.
Highlights
Membrane-bound proteins and peptides constitute a major class of all expressed proteins and peptides of a genome and are involved in crucial biological processes [1]
Many naturally occurring peptides bind to biological membranes, examples include peptide hormones, bacterial toxins and antimicrobial peptides [4,5,6] with the latter being probably the largest and best characterized group of them
Besides membrane-bound peptides, which can be structurally characterized by solution NMR spectroscopy, there are an enormous number of membrane-binding proteins
Summary
Membrane-bound proteins and peptides constitute a major class of all expressed proteins and peptides of a genome and are involved in crucial biological processes [1]. For -helical peptides the tilt and azimuth angle can be obtained from the resulting wave-like behavior of the saturation parameter of the spin-label as a function of position within the peptide This approach was applied, for example, to determine the orientation of the designed antimicrobial peptide CM15 in phosphatidylethanolamine and phosphatidylglycerol vesicles [86]. Another elegant EPR approach towards obtaining the topology of peptides in bilayers exploits the anisotropic hyperfine tensor of the nitroxide spin label 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) [87,88,89] This agent, which needs to be introduced by chemical synthesis into the studied peptide, is a rigid paramagnetic probe whose hyperfine splitting highly depends on the orientation in the magnetic field Fig. The peptides to be studied need to be chemically modified which is laborious but might influence the behavior in a hydrophobic environment
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
