Arginine Side‐Chain Hydrogen Exchange: Quantifying Arginine Side‐Chain Interactions in Solution

• Published in: Chemphyschem 2019-01, Vol.20 (2), p.252-259
• Main Authors: Mackenzie, Harold W., Hansen, D. Flemming
• Format: Article
• Language: English
• Subjects: 13C-detected NMR spectroscopy; Aqueous solutions; arginine side-chains; Chains; Crystal structure; Deuterium; Foreign exchange rates; guanidinium interactions; Hydrogen; Hydrogen atoms; hydrogen exchange; Lysozyme; Mathematical analysis; NMR; Nuclear magnetic resonance; Phase separation; protection factors; protein-protein interactions; Proteins
• ISSN: 1439-4235; 1439-7641; 1439-7641
• DOI: 10.1002/cphc.201800598

The rate with which labile backbone hydrogen atoms in proteins exchange with the solvent has long been used to probe protein interactions in aqueous solutions. Arginine, an essential amino acid found in many interaction interfaces, is capable of an impressive range of interactions via its guanidinium group. The hydrogen exchange rate of the guanidinium hydrogens therefore becomes an important measure to quantify side‐chain interactions. Herein we present an NMR method to quantify the hydrogen exchange rates of arginine side‐chain 1Hϵ protons and thus present a method to gauge the strength of arginine side‐chain interactions. The method employs 13C‐detection and the one‐bond deuterium isotope shift observed for 15Nϵ to generate two exchanging species in 1H2O/2H2O mixtures. An application to the protein T4 Lysozyme is shown, where protection factors calculated from the obtained exchange rates correlate well with the interactions observed in the crystal structure. The methodology presented provides an important step towards characterising interactions of arginine side‐chains in enzymes, in phase separation, and in protein interaction interfaces in general. Hydrogen swap shop: A method is presented to measure the hydrogen exchange rates of the labile guanidinium protons of arginine side‐chains in proteins and thus to quantify the strength of interactions formed by the arginine guanidinium group. The technique, which employs 13C‐detected NMR spectroscopy, is demonstrated on the 19 kDa T4 lysozyme where hydrogen exchange rates are measured for all the thirteen arginine side chains.