Selenomethionine as a probe of its environment in biological macromolecules
Date
2018
Authors
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Publisher
University of Delaware
Abstract
Selenium can be used as a surrogate atom to sulfur in nuclear magnetic resonance spectroscopy (NMR) in order to understand the biological properties of sulfur, such as that thiols as activating groups in thioester biochemistry and disulfide bonds make up structural features of proteins. The 77Se chemical shielding tensor is highly sensitive to the protein environment and can report on which molecular interactions and degrees of freedom are available for seleno-containing amino acids. Particularly, the substitution of methionine (Met, M) to selenomethionine (SeM) was consistently shown to have minimal impact on structure and dynamics. Therefore, SeM can be used as probe of its local environment in proteins. However, for biological systems, data interpretation has yet to be developed systematically for 77Se NMR to explain which variables most affect the spectra.
To start building a biological 77Se magnetic resonance databank we constructed a library of GB1 variants with a single SeM at dissimilar locations. X-ray crystallography was used to obtain a direct visualization of the local environment surrounding SeM in each variant at atomic resolution. The structures confirmed the conformational flexibility solvent exposed locations at Ile6 and Val29, as well as the local rigidities at Leu5 and Val39. The SeM sidechain at position 34 exists on a continuum of conformations stabilized by aromatic or nonpolar interactions. These structures are used as the basis for the development of DFT calculations to investigate the 77Se NMR parameters.