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

Summary, in English

We report here a method for the determination of the pK_a 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_a 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_a of interest.

• Author: Gabriel A. Braun; Brett H. Pogostin; Milda Pucetaite; Casey H. Londergan; Karin S. Åkerfeldt
• Department/s: Biochemistry and Structural Biology; BECC: Biodiversity and Ecosystem services in a Changing Climate; Centre for Environmental and Climate Science (CEC)
• Publishing year: 2020
• Language: English
• Pages: 1701-1705
• Publication/Series: Biophysical Journal
• Volume: 119
• Issue: 9
• Links: http://dx.doi.org/10.1016/j.bpj.2020.09.011
• Document type: Journal article
• Publisher: Cell Press
• Topic: Biophysics
• Status: Published
• ISBN/ISSN/Other: ISSN: 0006-3495