Protection from superoxide damage associated with an increased level of the YggX protein in Salmonella enterica - PubMed (original) (raw)

Protection from superoxide damage associated with an increased level of the YggX protein in Salmonella enterica

J Gralnick et al. Proc Natl Acad Sci U S A. 2001.

Abstract

The deleterious effect of superoxide radicals on cell growth and survival is predominantly caused by rapid oxidation of labile [Fe-S] clusters in proteins. Oxidation of these clusters releases Fe(II) ions, which participate in Fenton chemistry that damages DNA. Here it is shown that elevated levels of the YggX protein increase the resistance of Salmonella enterica to superoxide stress, reverse enzymatic defects attributed to oxidized [Fe-S] clusters, and decrease the spontaneous mutation frequency. The data are consistent with a model in which YggX protects protein [Fe-S] clusters from oxidation.

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Figures

Figure 1

Figure 1

Physical parameters of yggX and its gene product. (A) Alignment of YggX homologs. (B) Operon structure of mutY/yggX in E. coli and S. enterica LT2. Promoters were mapped by Gifford and Wallace in E. coli (43).

Figure 2

Figure 2

Increased levels of YggX protein in yggX* mutant. Western blot analysis was performed according to Harlow and Lane (59). Proteins were visualized by using alkaline phosphatase conjugated to anti-rabbit secondary antibody (Promega). Lanes A–C were loaded with crude cell-free extracts (1 μg protein) from strains DM5104, DM5105 (yggX*), and DM5647 (_yggX_∷Gm), respectively. Lane D was loaded with 1 ng purified YggX.

Figure 3

Figure 3

The yggX* mutation does not increase MNNG resistance of gshA mutants. Strain LT2 was grown in LB with (▴) and without (▵) 60 μM MNNG. Both gshA (○) and gshA yggX* (●) mutant strains were grown in LB with 60 μM MNNG.

Figure 4

Figure 4

The yggX* mutation increases resistance of S. enterica to PQ. (A) Growth of gshA (○) and gshA yggX* (●) mutant strains in LB with 4 μM PQ. (B) Growth of LT2 (▵) and yggX* (▴) strains in LB with 40 μM PQ.

Figure 5

Figure 5

yggX* does not require soxR to mediate resistance to PQ. Strains LT2 (♦), soxR (◊), and soxR yggX* (▾) were grown in LB with 4.0 μM PQ.

Figure 6

Figure 6

Model showing how YggX protects S. enterica from oxidative damage. The result of superoxide attack on [Fe-S] clusters is depicted. We hypothesize that YggX is able to block oxidative damage to labile clusters and thus prevent the normal downstream consequences of such oxidation.

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