Protein Aggregation in a Mutant Deficient in YajL, the Bacterial Homolog of the Parkinsonism-associated Protein DJ-1

Abstract

YajL is the closest prokaryotic homolog of the parkinsonismassociated protein DJ-1 (40% sequence identity and similar three-dimensional structure), a protein of unknown function involved in the cellular response to oxidative stress. We report here that a yajL mutant of Escherichia coli displays an increased sensitivity to oxidative stress. It also exhibits a protein aggregation phenotype in aerobiosis, but not in anaerobiosis or in aerobic cells overexpressing superoxide dismutase, suggesting that protein aggregation depends on the presence of reactive oxygen species produced by respiratory chains. The protein aggregation phenotype of the yajL mutant, which can be rescued by the wildtype yajL gene, but not by the corresponding cysteine 106 mutant allele, is similar to that of multiple mutants deficient in superoxide dismutases and catalases, although intracellular hydrogen peroxide levels were not increased in the yajL mutant, suggesting that protein aggregation in this strain does not result from a hydrogen peroxide detoxification defect. Aggregationprone proteins included 17 ribosomal proteins, the ATP synthase ␤ subunit, flagellin, and the outer membrane proteins OmpA and PAL; all of them are part of multiprotein complexes, suggesting that YajL might be involved in optimal expression of these complexes, especially during oxidative stress. YajL stimulated the renaturation of urea-unfolded citrate synthase and the solubilization of the urea-unfolded ribosomal proteins S1 and L3 and was more efficient as a chaperone in its oxidized form than in its reduced form. The mRNA levels of several aggregated proteins of the yajL mutant were severely affected, suggesting that YajL also acts at the level of gene expression. These two functions of YajL might explain the protein aggregation phenotype of the yajL mutant.

YajL, Prokaryotic Homolog of Parkinsonism-associated Protein DJ-1, Functions as a Covalent Chaperone for Thiol Proteome

“…In both DJ-1 and YajL, cysteine 106 is required for protecting cells against oxidative stress (7,19). It is easily oxidizable to a sulfenic acid form, but it is not clear whether this oxidation is important for the function of these proteins, or whether it is incidental or even detrimental (19).…”

“…Both YajL and DJ-1 lack the Cys, His, Asp/Glu putative catalytic triad, and their nucleophilic elbow cysteine is oxidized in crystals to cysteine sulfenic or sulfinic acid (6,8,9). This conserved cysteine is crucial for the protective functions of DJ-1 and YajL against oxidative stress (3,4,7). Many biochemical functions have been proposed for DJ-1.…”

“…All members of this superfamily contain a similar domain with a nucleophilic elbow displaying an important cysteine (Cys-106 in DJ-1 and YajL) that is part of a Cys, His, Glu/Asp catalytic triad in the peptidases PfpI and Hsp31 3 (5,6). In other members of the family, such as DJ-1 and YajL, this Cys residue plays an important role in oxidative stress resistance (3,4,7).…”

“…In vivo studies of the DJ-1 chaperone activity produced mixed results (10,18) so that the significance of this function in protecting cells against oxidative stress is not yet clear (19). YajL exhibits a chaperone activity toward citrate synthase and the ribosomal proteins S1 and L3, and protein aggregation occurs in the yajL mutant under aerobic conditions but not in anaerobiosis (7).…”

“…It has been suggested to function as a weak protease (4), an oxidative stress-activated chaperone (6,10,11), an atypical peroxiredoxin-like peroxidase that scavenges H 2 O 2 (12), a stabilizer of the antioxidant transcriptional regulator Nrf2 (13), an apoptosis inhibitor via its interaction with Daxx (14), a transcriptional or translational (4, 15) regulator of gene expression, and a regulator of uncoupling protein expression affecting mitochondrial potential and production of reactive oxygen species (16). YajL protects bacteria against oxidative stress and oxidative stress-induced protein aggregation, possibly through its chaperone function and control of gene expression (7). Moreover, yajL mutants display translational accuracy defects (17).…”