Research ArticleCell Biology

Spatial and temporal alterations in protein structure by EGF regulate cryptic cysteine oxidation

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Science Signaling  21 Jan 2020:
Vol. 13, Issue 615, eaay7315
DOI: 10.1126/scisignal.aay7315

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Uncovering cryptic cysteine residues for oxidation

Growth factor signaling results in the generation of reactive oxygen species (ROS) that oxidize cysteine residues in target proteins, triggering changes in activity, localization, or abundance. A long-standing question is how different growth factors specify the oxidation of cysteine residues in distinct subsets of proteins. Behring et al. found that many oxidized cysteine residues in target proteins were buried and not accessible under basal conditions. EGF stimulation altered the conformation of the target proteins through phosphorylation or nucleotide substrate flux, exposing the cryptic cysteine residues and enabling their oxidation. Thus, growth factor–mediated redox regulation of cysteine residues may be determined by changes in target protein conformation that occur in a pathway-specific manner.

Abstract

Stimulation of plasma membrane receptor tyrosine kinases (RTKs), such as the epidermal growth factor receptor (EGFR), locally increases the abundance of reactive oxygen species (ROS). These ROS then oxidize cysteine residues in proteins to potentiate downstream signaling. Spatial confinement of ROS is an important regulatory mechanism of redox signaling that enables the stimulation of different RTKs to oxidize distinct sets of downstream proteins. To uncover additional mechanisms that specify cysteines that are redox regulated by EGF stimulation, we performed time-resolved quantification of the EGF-dependent oxidation of 4200 cysteine sites in A431 cells. Fifty-one percent of cysteines were statistically significantly oxidized by EGF stimulation. Furthermore, EGF induced three distinct spatiotemporal patterns of cysteine oxidation in functionally organized protein networks, consistent with the spatial confinement model. Unexpectedly, protein crystal structure analysis and molecular dynamics simulations indicated widespread redox regulation of cryptic cysteine residues that are solvent exposed only upon changes in protein conformation. Phosphorylation and increased flux of nucleotide substrates served as two distinct modes by which EGF specified the cryptic cysteine residues that became solvent exposed and redox regulated. Because proteins that are structurally regulated by different RTKs or cellular perturbations are largely unique, these findings suggest that solvent exposure and redox regulation of cryptic cysteine residues contextually delineate redox signaling networks.

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