Glutaredoxins are essential for stress adaptation in the cyanobacterium Synechocystis sp. PCC 6803

Abstract

Glutaredoxins are small redox proteins able to reduce disulfides and mixed disulfides between GSH and proteins. Synechocystis sp. PCC 6803 contains three genes coding for glutaredoxins: ssr2061 (grxA) and slr1562 (grxB) code for dithiolic glutaredoxins while slr1846 (grxC) codes for a monothiolic glutaredoxin. We have analyzed the expression of these glutaredoxins in response to different stresses, such as high light, H2O2 and heat shock. Analysis of the mRNA levels showed that grxA is only induced by heat while grxC is repressed by heat shock and is induced by high light and H2O2. In contrast, grxB expression was maintained almost constant under all conditions. Analysis of GrxA and GrxC protein levels by western blot showed that GrxA increases in response to high light, heat or H2O2 while GrxC is only induced by high light and H2O2, in accordance with its mRNA levels. In addition, we have also generated mutants that have interrupted one, two, or three glutaredoxin genes. These mutants were viable and did not show any different phenotype from the WT under standard growth conditions. Nevertheless, analysis of these mutants under several stress conditions revealed that single grxA mutants grow slower after H2O2, heat and high light treatments, while mutants in grxB are indistinguishable from WT. grxC mutants were hypersensitive to treatments with H2O2, heat, high light and metals. A double grxAgrxC mutant was found to be even more sensitive to H2O2 than each corresponding single mutants. Surprisingly a mutation in grxB suppressed totally or partially the phenotypes of grxA and grxC mutants except the H2O2 sensitivity of the grxC mutant. This suggests that grxA and grxC participate in independent pathways while grxA and grxB participate in a common pathway for H2O2 resistance. The data presented here show that glutaredoxins are essential for stress adaptation in cyanobacteria, although their targets and mechanism of action remain unidentified.

Responses to Oxidative and Heavy Metal Stresses in Cyanobacteria: Recent Advances

“…Some monothiol Grxs have also been reported to catalyze protein deglutathionylation [ 67 ]. The poorly understood cyanobacterial Grxs are studied in Synechocystis PCC6803 because it possesses only three Grxs, which are all are dispensable to cell growth under standard photoautotrophic conditions [ 14 , 68 ]. The dithiol enzymes Grx1 (Slr1562, also known as GrxB) and Grx2 (Ssr2061, also known as GrxA) operate in the tolerance to arsenate [ 54 , 55 ].…”

“…Emphasizing on the crosstalk between the Grx and Trx systems, we found that Grx1 and Grx2 operate in an integrative redox pathway, NAD(P)H-thioredoxin reductase–Grx1–Grx2–ferredoxin 7, which transfer electrons in that order, to reduce selenate [ 60 ]. The Grx2 enzyme also operates in the tolerance to H 2 O 2 [ 60 , 68 ] and heat shock [ 68 ].…”

Glutaredoxin 1 Deficiency Leads to Microneme Protein-Mediated Growth Defects in Neospora caninum

“…The main reason for the slow growth in mutations of Grx2 may be the influence of Fe-S cluster metabolism in the nitrogenase complex assembly ( Benyamina et al, 2013 ). In many organisms, including yeast, Synechocystis , Arabidopsis thaliana , mouse, and human, disruption of Grx caused highly sensitive to stress-induced oxidative damage, indicating that Grx plays an important role in stress adaptation ( Rodríguez-Manzaneque et al, 2002 ; Lillig et al, 2004 ; Chung et al, 2005 ; Cheng, 2008 ; Mühlenhoff et al, 2010 ; Wu et al, 2011 ; Sánchez-Riego et al, 2013 ). In this study, the loss of NcGrx1 caused growth-inhibition of parasites under oxidative stress (H 2 O 2 ) condition, which indicated that NcGrx1 is crucial for maintaining redox balance in N. caninum under oxidative stress.…”

Global analysis of the RpaB regulon based on the positional distribution of HLR1 sequences and comparative differential RNA-Seq data

“…RpaB seems to regulate most genes of the glutathione/glutaredoxin system, relevant to prevent photooxidative damage. GrxA and GrxC were reported to be the only HL-inducible glutaredoxins, serving as electron acceptors of glutathione (63).…”