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Probing conformational propensities of histidine in different protonation states of the unblocked glycyl‐histidyl‐glycine peptide by vibrational and NMR spectroscopy
Author(s) -
DiGuiseppi David,
SchweitzerStenner Reinhard
Publication year - 2016
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.4885
Subject(s) - polyproline helix , chemistry , protonation , histidine , ramachandran plot , tripeptide , crystallography , peptide , nuclear magnetic resonance spectroscopy , circular dichroism , side chain , stereochemistry , dihedral angle , protein structure , hydrogen bond , amino acid , molecule , organic chemistry , ion , biochemistry , polymer
Histidine has been shown to play a major role in a number of biological systems. Being able to understand unconstrained conformational distributions of histidine and their dependence on the environment can shed light on the structure–function relation with regard to its multiple roles in biochemical processes such as proton transfer, ligand binding, protein folding and maintaining protein intrinsic disorder. We utilized polarized Raman, FTIR, vibrational circular dichroism and 1 H NMR spectroscopy to probe the conformational distribution of the central histidine in the unblocked tripeptide H‐Gly‐His‐Gly‐OH in D 2 O. Our results show that in the double protonated state (GHG ++ ), 94% of the histidine residue resides in the upper left quadrant of the Ramachandran plot with an equal partition between polyproline II (pPII) and β‐strand conformations. In this protonation state, enthalpic and entropic differences between the two conformations are practically eliminated, which indicates reduced backbone and/or side chain hydration. On the contrary, the single protonated state (GHG + ), while only marginally different with regard to the pPII/β partition at room temperature (β‐strand is now slightly favored), shows an enthalpic stabilization of pPII by 43.02 kJ/mol, which is being compensated by an entropic stabilization of β‐strand (0.145 kJ/(mol K)). This indicates a much stronger coupling between peptide and water. At neutral pH, where the imidazole side chain of the histidine residue is deprotonated, GHG in D 2 O forms a hydrogel above a peptide concentration of approximately 25 m m . Some experimental evidence suggests that the preceding peptide aggregation involves hydrogen bonding between the C‐terminal groups and the imidazole NH group. Copyright © 2016 John Wiley & Sons, Ltd.