Avicinylation (thioesterification): A protein modification that can regulate the response to oxidative and nitrosative stress

Abstract

Avicins are a recently discovered family of plant-derived terpenoid molecules that possess proapoptotic, antiinflammatory, and cytoprotective properties in mammalian cells. Previous work demonstrating that avicins can exert their effects by suppressing or activating the redox-sensitive transcription factors NF-B and nuclear factor-erythroid 2 p45-related factor (Nrf2), respectively, has raised the idea that they may react with critical cysteine residues. To understand the molecular mechanism through which avicins regulate protein function, we examined their effects on the paradigmatic redox-responsive transcriptional activator, OxyR of Escherichia coli, which protects bacterial cells against oxidative and nitrosative stresses. In vitro transcription assays demonstrated that avicins activate OxyR and its target genes katG and oxyS in a DTT-reversible manner. In addition, katG-dependent hydroperoxidase I activity was enhanced in avicin-treated bacteria. Mass spectrometric analysis of activated OxyR revealed thioesterification of the critical regulatory cysteine, Cys-199, to an avicin fragment comprising the outer monoterpene side chain. Our results indicate that avicinylation can induce adaptive responses that protect cells against oxidative or nitrosative stress. More generally, transesterification may represent a previously undescribed thioldirected posttranslational modification, which extends the code for redox regulation of protein function.cysteine ͉ terpenes ͉ thioester ͉ OxyR ͉ redox C lassic signal transduction is characterized by ligand-induced stimulation of pathways comprised of interconnected groups of proteins that undergo various regulatory modifications. Redox-based signaling usually involves small reactive molecules, which covalently and reversibly modify specific cysteine targets to regulate multiple cell processes, including cell proliferation, differentiation, and apoptosis (1). Recent work has demonstrated a significant interface that connects a prototypic redoxrelated signaling process, S-nitrosylation, with ligand-induced signaling involving multiprotein complexes (2, 3), and accumulating evidence suggests that malfunction in redox-based signaling may underlie disease pathogenesis (4-7). Hence, redox regulation may play an important role in normal physiology, as well as in a growing list of medical disorders.Cells adapt to various forms of stress in part by activating redox-responsive genes, which encode proteins involved in detoxification, repair, and maintenance of homeostasis. Several classes of redox-sensitive transcription factors have been shown to regulate the expression of these genes (8). Studies designed to elucidate the mechanism by which such transcription factors are regulated have revealed the importance of critical cysteine residues, which play sensory as well as regulatory roles in transcriptional responses. In particular, cysteine thiols in transcription factors have been shown to exhibit highly selective and differential reactivity toward different reactive oxygen or nitrog...

Peroxide‐Sensing Transcriptional Regulators in Bacteria

“…Initially, this was based primarily on in vitro studies indicating that oxidative modification of only C199 was sufficient for activation, since hydroxylated Cys199-SOH, S-nitrosylated (Cys199-SNO), and S-glutathionylated (Cys199-S-S-G) forms of OxyR were able to activate transcription, and that the different modifications elicited distinct changes in the circular dichroism (CD) spectra of OxyR-DNA complexes (40,56). The idea was subsequently reinforced by the observation that Cys199-thiol-esterification of OxyR resulted in activation of target genes both in vitro and in vivo (38). Until recently, there were little available data to adequately evaluate the molecular code model's prediction of modification-specific patterns of gene activation.…”

Terpenoids: natural inhibitors of NF-κB signaling with anti-inflammatory and anticancer potential

“…Moreover, the treatment of cells with dithiothreitol (DTT) could reverse the avicin G-induced inhibition in DNA binding of NF-kB complex. This is due to the ability of avicins to cause thioesterification, also called avicinylation, of the cysteine residue in the DNA-binding domain of the NF-kB protein [122]. The amount of avicin in plants is dependent on stress insults, and hence different stress models in in vitro cultures have been established to achieve biomass production of avicins.…”

Redox-based regulation of signal transduction: Principles, pitfalls, and promises

“…Recent studies have shown that the sulfinic acid form of 2-cys peroxiredoxins can be reduced back to the sulfhydryl in an ATP-dependent enzyme-(sulfiredoxin, Srx) catalyzed reaction [39], and a reversible thioesterifcation has been reported to alter transcriptional activity [40], raising the possibility that additional Cys modifications may be found to have regulatory roles. Cysteines also are uniquely targeted by alkylating species (such as cyclopentenone prostaglandins, acrolein), hydroxynonenal and avicins (which can be formed endogenously, or encountered through environmental insults [41,42]), and by acylation (which has important roles in localizing proteins to the membranes [43]).…”