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A covalent bond links lysine and cysteine in proteins together under oxidizing conditions, stabilizing them

A paper titled "Functional implications of unusual NOS and SONOS covalent linkages found in proteins," by Matthew D. Lloyd, Kyle S. Gregory, and K. Ravi Acharya, from the University of Bath Department of Life Sciences, has been in Chemical Communications.

Proteins are formed in cells by linking amino acid building blocks together in a defined sequence. There are 20 different amino acids that are used to build proteins, including cysteine and lysine, which are involved in the formation of this type of bond.

Proteins have a wide range of different roles in cells, such as maintaining cell structure, regulating the passage of materials in and out of the cell, controlling signaling events, and performing chemical reactions. The performance of these roles requires that the protein is folded into a particular shape. The folded shape is maintained by a series of forces and bonds, including certain types of covalent bonds where atoms in different amino acids in the protein are physically joined together.

The most well-known of these covalent bonds which keep proteins folded are disulfide bonds. The type of bond highlighted in this paper is known as a NOS bond. These new bonds were only discovered in 2016, and are formed when the end of a lysine side-chain is linked to the end of a cysteine side-chain with an oxygen atom linking them together.

The NOS bond is formed under oxidizing conditions. So far, all examples of this type of bond have been identified using protein crystallography, where X-rays are used to image the folded protein structure. The NOS bond is found in many viral, bacterial, and human proteins, including botulism toxins.

The NOS bonds are formed when cells experience oxidative stress, but their significance is not well understood. Recent studies have shown that the function of enzymes (proteins that perform chemical reactions) can be significantly reduced when NOS bonds are formed. It is likely that the function of other types of protein will also be modified by the presence of the NOS bond. Moreover, NOS bonds are likely to influence how damaged proteins are cleared from cells and have a role in disease processes.

Understanding these effects will enable researchers to understand their basic biology and how these effects change in disease, and may eventually enable the development of new treatments.