Cysteine thiol sulfinic acid in plant stress signaling

Abstract

Cysteine thiols are susceptible to various oxidative posttranslational modifications (PTMs) due to their high chemical reactivity. Thiol‐based PTMs play a crucial role in regulating protein functions and are key contributors to cellular redox signaling. Although reversible thiol‐based PTMs, such as disulfide bond formation, S‐nitrosylation, and S‐glutathionylation, have been extensively studied for their roles in redox regulation, thiol sulfinic acid (–SO2H) modification is often perceived as irreversible and of marginal significance in redox signaling. Here, we revisit this narrow perspective and shed light on the redox regulatory roles of –SO2H in plant stress signaling. We provide an overview of protein sulfinylation in plants, delving into the roles of hydrogen peroxide‐mediated and plant cysteine oxidase‐catalyzed formation of –SO2H, highlighting the involvement of –SO2H in specific regulatory signaling pathways. Additionally, we compile the existing knowledge of the –SO2H reducing enzyme, sulfiredoxin, offering insights into its molecular mechanisms and biological relevance. We further summarize current proteomic techniques for detecting –SO2H and furnish a list of experimentally validated cysteine –SO2H sites across various species, discussing their functional consequences. This review aims to spark new insights and discussions that lead to further investigations into the functional significance of protein –SO2H‐based redox signaling in plants.

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“…Unlike other ROS, H2O2 has a relatively long half-life (milliseconds to seconds) and high activation energy which makes it stable enough to diffuse and generate gradients from its source and react selectively with protein metal centres and specialised thiols (Waszczak et al, 2015;Willems et al, 2023). Its unique physico-chemical properties and highly regulated production and detoxification position H2O2 in the centre of the cellular redox homeostasis and signalling (Huang et al, 2024). The reaction of H2O2 with cysteine thiols first results in the formation of highly an unstable sulfenic acid (-SOH) which can be further oxidized to sulfinic (-SO2H) or sulfonic acid (-SO3H), or can react with other cysteine residues, forming disulfide bonds (Akter et al, 2018;Huang et al, 2021).…”