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Deuterium-Enhanced Raman Spectroscopy for Histidine pKa Determination in a pH-Responsive Hydrogel

Braun, Gabriel A. LU ; Pogostin, Brett H. ; Pucetaite, Milda LU ; Londergan, Casey H. and Åkerfeldt, Karin S. LU (2020) In Biophysical Journal 119(9). p.1701-1705
Abstract

We report here a method for the determination of the pKa of histidine in complex or heterogeneous systems amenable to neither solid-state nor solution NMR spectroscopy. Careful synthesis of a fluorenylmethyloxycarbonyl- and trityl-protected, C2-deuterated histidine produces a vibrational-probe-equipped amino acid that can readily be incorporated into any peptide accessible by standard solid-phase methods. The frequency of the unique, Raman-active stretching vibration of this C2-D probe is a clear reporter of the protonation state of histidine. We investigate here a pH-sensitive peptide that self-assembles to form a hydrogel at neutral pH. The pKa of the lone histidine residue in the peptide, which is likely... (More)

We report here a method for the determination of the pKa of histidine in complex or heterogeneous systems amenable to neither solid-state nor solution NMR spectroscopy. Careful synthesis of a fluorenylmethyloxycarbonyl- and trityl-protected, C2-deuterated histidine produces a vibrational-probe-equipped amino acid that can readily be incorporated into any peptide accessible by standard solid-phase methods. The frequency of the unique, Raman-active stretching vibration of this C2-D probe is a clear reporter of the protonation state of histidine. We investigate here a pH-sensitive peptide that self-assembles to form a hydrogel at neutral pH. The pKa of the lone histidine residue in the peptide, which is likely responsible for this pH-dependent behavior, cannot be investigated by NMR spectroscopy because of the supramolecular, soft nature of the gel. However, after synthesizing a C2-deuterated-histidine-containing peptide, we were able to follow the protonation state of histidine throughout a pH titration using Raman difference spectroscopy, thereby precisely determining the pKa of interest.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Biophysical Journal
volume
119
issue
9
pages
1701 - 1705
publisher
Cell Press
external identifiers
  • scopus:85092788691
  • pmid:33080220
ISSN
0006-3495
DOI
10.1016/j.bpj.2020.09.011
language
English
LU publication?
yes
id
ede2ad87-ec15-4a5c-9ed1-022182242b8f
date added to LUP
2020-10-26 09:23:42
date last changed
2021-05-11 03:51:13
@article{ede2ad87-ec15-4a5c-9ed1-022182242b8f,
  abstract     = {<p>We report here a method for the determination of the pK<sub>a</sub> of histidine in complex or heterogeneous systems amenable to neither solid-state nor solution NMR spectroscopy. Careful synthesis of a fluorenylmethyloxycarbonyl- and trityl-protected, C2-deuterated histidine produces a vibrational-probe-equipped amino acid that can readily be incorporated into any peptide accessible by standard solid-phase methods. The frequency of the unique, Raman-active stretching vibration of this C2-D probe is a clear reporter of the protonation state of histidine. We investigate here a pH-sensitive peptide that self-assembles to form a hydrogel at neutral pH. The pK<sub>a</sub> of the lone histidine residue in the peptide, which is likely responsible for this pH-dependent behavior, cannot be investigated by NMR spectroscopy because of the supramolecular, soft nature of the gel. However, after synthesizing a C2-deuterated-histidine-containing peptide, we were able to follow the protonation state of histidine throughout a pH titration using Raman difference spectroscopy, thereby precisely determining the pK<sub>a</sub> of interest.</p>},
  author       = {Braun, Gabriel A. and Pogostin, Brett H. and Pucetaite, Milda and Londergan, Casey H. and Åkerfeldt, Karin S.},
  issn         = {0006-3495},
  language     = {eng},
  number       = {9},
  pages        = {1701--1705},
  publisher    = {Cell Press},
  series       = {Biophysical Journal},
  title        = {Deuterium-Enhanced Raman Spectroscopy for Histidine pK<sub>a</sub> Determination in a pH-Responsive Hydrogel},
  url          = {http://dx.doi.org/10.1016/j.bpj.2020.09.011},
  doi          = {10.1016/j.bpj.2020.09.011},
  volume       = {119},
  year         = {2020},
}