Hydration of the Gly2 and Gly3 peptide oxygens of [Leu5]‐enkephalin in aqueous solution as revealed by the combined use of ¹⁷O‐NMR and Fourier‐transform infrared spectroscopy

Abstract

Solvent-induced and temperature-induced ' 0 chemical shifts of , LeuSI-enkephalin and solvent-induced spectral modifications of the amide-I' stretching vibrations of [1-13C-Gly2, Leu51-enkephalin and [1-13C-Gly2, Leu51-enkephalin are reported and correlated with the spectroscopic characteristics of model amides. It is demonstrated that both Gly2 and Gly3 peptide oxygens are motionally equivalent and form solvation species which are essentially monohydrated in aqueous solution, contrary to several simple amides and model peptides in which water largely forms dihydrates. It is shown that the combined use of 170-NMR and Fourier transform infrared is a unique methodology for studying the hydration state of specific peptide oxygens in peptide hormones.Peptides and proteins in biological systems are usually surrounded by a predominantly aqueous solvent. Their small size, large dipole moment and high capacity for forming hydrogen bonds means that the water molecules have unique effects on peptide and protein conformations [l -31. Hydrogen-bonding interactions between the oxygen atom of the peptide groups and the molecules of water undoubtedly contribute to the overall conformational stability of peptides and proteins in aqueous medium. The knowledge of these solvent interactions is of importance for any conformational study since it is known that biomolecules often change their conformation as the solvent is varied.As a first step towards the solution of hydration of peptides and proteins, numerous experimental and theoretical investigations on the most probable sites for binding of the water molecules have been undertaken on amides [4-lo]. These molecules are considered as the simplest representatives of the peptide bond; therefore, the determination of the possible monohydrated and multihydrated species has been considered as crucial in gauging the magnitude of specific hydration of more complex peptides and proteins. Furthermore, several theoretical calculations of model peptides [11 -201 and numerous X-ray structural investigations of several peptide hydrates and proteins [21-281 revealed thermodynamical and geometrical aspects of peptide-backbone hydration.

Oligomerization and Aggregation of Bovine Pancreatic Ribonuclease A:Backbone Hydration Probed by Infrared Band-Shift

“…Meanwhile, the loss of regular secondary structures could be monitored by the intensity changes of the amide I band. This correlation has been well-studied in helical peptides [22][23][24][25]27], but is addressed in limited numbers of proteins composing various secondary structures. To verify the hypothesis concerning band frequency and hydration states above, we studied the behavior of the thermal transition of RNase A as a model system.…”

“…More importantly, it has long been recognized that the IR amide bands are affected by the microenvironments of the secondary structures [21]. Since the carbonyl oxygen groups of polypeptides can form hydrogen bonds with water during protein hydration, the peak-shift of the amide I band provides a means to monitor the hydration states of secondary structures and this has recently been applied to reflect the extent of hydration in the thermal transition of -helical peptides [22][23][24][25][26][27]. These studies revealed a good correlation of the movement of the IR band from the -helix and the solvation of peptide backbone at low temperatures.…”

Oxygen-17 NMR spectroscopy: Basic principles and applications (Part I)

“…c The trans isomer which largely exists in a b-turn intramolecular hydrogen bonded form [311]. d The peptide oxygens are supposed to form largely monohydrates [312,313]. Care has to be taken, however, in using these correlations, because they are restricted to special applications.…”

Oxygen-17 NMR spectroscopy: Basic principles and applications (part II)

“…167). For Gerothanassis et al [313,775] investigated in detail Leuenkephalin (Tyr-Gly-Gly-Phe-Leu) which is a brain neurotransmitter peptide that has been extensively investigated during the past 30 years with a variety of spectroscopic methods. Both ( 17 O-Gly2, Leu5)-enkephalin and ( 17 O-Gly3, Leu5)-enkephalin have similar 17 O chemical shifts in CH 3 CNADMSO (4:1; vol.)…”