An essential thioredoxin is involved in the control of the cell cycle in the bacterium Caulobacter crescentus

Abstract

Thioredoxins (Trxs) are antioxidant proteins that are conserved among all species. These proteins have been extensively studied and perform reducing reactions on a broad range of substrates. Here, we identified Caulobacter crescentus Trx1 (CCNA_03653; CcTrx1) as an oxidoreductase that is involved in the cell cycle progression of this model bacterium and is required to sustain life. Intriguingly, the abundance of CcTrx1 varies throughout the C. crescentus cell cycle: while the expression of CcTrx1 is induced in stalked cells, right before DNA replication initiation, CcTrx1 is actively degraded by the ClpXP protease in predivisional cells. Importantly, we demonstrated that regulation of the abundance of CcTrx1 is crucial for cell growth and survival as modulating CcTrx1 levels leads to cell death. Finally, we also report a comprehensive biochemical and structural characterization of this unique and essential Trx. The requirement to precisely control the abundance of CcTrx1 for cell survival underlines the importance of redox control for optimal cell cycle progression in C. crescentus. INTRODUCTIONThioredoxins (Trx) are small antioxidant proteins that have been identified in most living organisms. They receive electrons from NADPH through the flavoprotein thioredoxin reductase and catalyze the reduction of oxidized cysteine residues in substrate proteins (1). As such, they are implicated in a variety of processes, ranging from oxidative stress defense to signal transduction. These soluble proteins all share a similar structure, a Trx-fold consisting of five b-strands surrounded by 4 ahelices. They also display a strictly conserved WCGPC catalytic active site motif and contain a cis-proline residue (1). The two cysteines of the catalytic motif are the key players involved in the reduction of oxidized substrates.First identified in 1964 as an electron donor for ribonucleotide reductase (2,3), Escherichia coli Trx1 (EcTrx1) is a major http://www.jbc.org/cgi

The Chaperone and Redox Properties of CnoX Chaperedoxins Are Tailored to the Proteostatic Needs of Bacterial Species

“…5f ). Finally, overexpression of Cc CnoX suppressed the essentiality of Cc Trx1 ( Table 1 ), a C. crescentus Trx protein with a WCGPC motif that we recently characterized as essential ( 31 ) (see Discussion). In combination, these results reveal that Cc CnoX is a real Trx oxidoreductase that functions in a classical reducing pathway.…”

“…The identification of 90 redox substrates of Cc CnoX ( Table S1 ) agrees with this idea. We previously reported that Cc Trx1, the only single-domain Trx expressed by C. crescentus , is essential—probably because it is responsible for the recycling of ribonucleotide reductase ( 31 ), the essential enzyme that catalyzes the reduction of ribonucleotides to their corresponding deoxyribonucleotides ( 36 ). Since Cc CnoX does not rescue the growth of the nonviable Δ Cctrx1 mutant unless overexpressed ( Table 1 ), the two proteins likely have different substrate specificities.…”

“…In comparison, E. coli encodes two single-domain Trxs and three dithiol-glutaredoxins ( 38 ). In addition, in C. crescentus , Cc Trx1 is thought to play a rather specific role, with expression levels that vary throughout the cell cycle: while the expression of Cc Trx1 is induced before DNA replication initiation, the protein is actively degraded by the ClpXP protease in predivisional cells ( 31 ). In contrast, the expression of Cc CnoX is not cell cycle regulated (data not shown).…”

Untargeted metabolomics links glutathione to bacterial cell cycle progression

“…Likewise, yeast DNA synthesis is temporally confined to the more reductive phase of the YMC 65 . Notably also, C. crescentus displays thioredoxin (Trx1) peak expression during S phase 66 and an overall redox shift during cell cycle progression 67 .…”

Cell cycle-controlled clearance of the CcrM DNA methyltransferase by Lon is dependent on DNA-facilitated proteolysis and substrate polar sequestration

“…The activation of NstA requires dimerization by formation of intermolecular cysteine disulfide bonds under oxidizing conditions in early S phase. Trx1 was recently reported to be specifically induced in early S phase to counteract oxidizing stress (Goemans et al, 2018). CcrM contains two conserved cysteines (C13 and C329), of which the latter is located in a motif that is critical for DNA binding activity.…”