Proteins are composed of long chains of amino acids, and a majority of these proteins have one or more methionine, a sulfur-containing amino acid.
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Within methionine, the oxidation of the sulfur atom is believed to be a major biomolecular reaction that could have a wide range of biological outcomes based on the context and the type of protein involved.
Fascinatingly, the sulfur oxidation of methionine can lead to two distinct versions of the oxidized molecule, that is, methionine sulfoxide, which differs only in the 3D spatial arrangement of its atoms. Both these versions are referred to as stereoisomers, or, more accurately, as diastereomers, which are stereoisomers but are not mirror images.
Scientists focused on the biological impacts of the oxidation of sulfur would prefer to isolate both stereoisomers, but this was almost impossible to achieve.
At the University of California, Santa Cruz (UC Santa Cruz), chemists have now reported an innovative technique for separating the methionine sulfoxide diastereomers, thus paving the way for analyzing their roles in major biological processes.
In a study published in Chemistry-A European Journal on April 6th, 2020, the researchers reported that they have successfully obtained both stereoisomers in purities of more than 99%.
The field of methionine oxidation has been hampered for decades by a lack of robust access to these reagents, and we believe this will be a tremendous boost.”
Jevgenij Raskatov, Study First Author and Assistant Professor, Department of Chemistry and Biochemistry, University of California, Santa Cruz
Raskatov’s laboratory teamed up with scientists from the California Institute of Technology for this study, which appeared on the cover of the journal. Raskatov informed that he had already heard from other scientists who have shown their interest in the latest method.
Raskatov’s research team employed a sophisticated chromatography method, known as supercritical fluid chromatography, in an attempt to purify the methionine sulfoxide stereoisomers. Supercritical fluids exhibit the characteristics of both liquids and gases, which can be quite handy in chromatography.
Then, using X-ray crystallography, the scientists also looked at the structures of the purified stereoisomers and confirmed their extraordinary stereochemical stability.
Apart from Raskatov, the study’s co-authors include Scott Virgil and Lawrence Henling from the California Institute of Technology, and Hsiau-Wei Lee, Ka Chan, Ariel Kuhn, and Alejandro Foley from UC Santa Cruz.
Raskatov, J. A., et al. (2020) A Facile Method for the Separation of Methionine Sulfoxide Diastereomers, Structural Assignment, and DFT Analysis. Chemistry–A European Journal. doi.org/10.1002/chem.201904848.