Phosphorylation of proteins has usually been considered as the insertion of a phosphorous group into a protein that turns it on or off.

"With this paper, we've elevated protein sulfenylation from a marker of oxidative stress to a bona fide reversible post translational modification that plays a key regulatory role during cell signaling," said Kate Carroll, a Scripps Research associate professor who led the study. "The sulfenyl modification is the new kid on the block."
During periods of cellular stress, caused by factors such as exposure to UV radiation or chronic disease states like cancer, the level of highly reactive oxygen-containing molecules can increase, resulting in inappropriate modification of proteins and cell damage. In sulfenylation, one oxidant, hydrogen peroxide, functions as a messenger that can activate cell proliferation through oxidation of cysteine residues in signaling proteins, producing sulfenic acid. Cysteine, an amino acid (natural protein building block), is highly oxidant sensitive.
Conventional wisdom has long held that if hydrogen peroxide does exist in the cell at any appreciable level, it represents a disease state, not a regulatory event. The new study shows that sulfenylation is actually a positive protein modification, and that it's required for signaling through the pathway, a validation of a long-held belief in some scientific circles that hydrogen peroxide functions as a general signaling molecule, not an oxidative "bad boy" to be eliminated at all costs.
A New Chemical Probe
To explore the process, Carroll and her colleagues developed a highly selective chemical probe -- known as DYn-2 -- with the ability to detect minute differences in sulfenylation rates within the cell.
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The technology described in the new paper is unique, Carroll said, because it allows scientists to trap and detect these modifications in situ, without interfering with the redox balance of the cell. "Probing cysteine oxidation in a cell lysate is like looking for a needle in a haystack," she said, "our new approach preserves labile sulfenyl modifications and avoids protein oxidation artifacts that arise during cell homogenization."
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Another broad impact of these findings, Carroll said, is to open up an entirely new mechanism to exploit for the development of therapeutics, particularly in cancer. "It should influence the design of inhibitors that target oxidant-sensitive cysteine residues in the future," she said.
Source-Eurekalert