A Novel Mechanism for Nitrosative Stress Tolerance Dependent on GTP Cyclohydrolase II Activity Involved in Riboflavin Synthesis of Yeast

Streptococcus mutans appears to possess a sole iron-sulfur (Fe-S) cluster biosynthesis system encoded by the sufCDSUB cluster. This study was designed to examine the role of sufCDSUB in S. mutans physiology. Allelic exchange mutants deficient of the whole sufCDSUB cluster and in individual genes were constructed. Compared to the wild-type, UA159, the sufCDSUB-deficient mutant, Δsuf::kanr, had a significantly reduced growth rate, especially in medium with the absence of isoleucine, leucine or glutamate/glutamine, amino acids that require Fe-S clusters for biosynthesis and when grown with medium adjusted to pH 6.0 and under oxidative and nitrosative stress conditions. Relative to UA159, Δsuf::kanr had major defects in stress tolerance responses with reduced survival rate of > 2-logs following incubation at low pH environment or after hydrogen peroxide challenge. When compared to UA159, Δsuf::kanr tended to form aggregates in broth medium and accumulated significantly less biofilm. As shown by luciferase reporter fusion assays, the expression of sufCDSUB was elevated by > 5.4-fold when the reporter strain was transferred from iron sufficient medium to iron-limiting medium. Oxidative stress induced by methyl viologen increased sufCDSUB expression by > 2-fold, and incubation in a low pH environment led to reduction of sufCDSUB expression by > 7-fold. These results suggest that lacking of SufCDSUB in S. mutans causes major defects in various cellular processes of the deficient mutant, including growth, stress tolerance responses and biofilm formation. In addition, the viability of the deficient mutant also suggests that SUF, the sole Fe-S cluster machinery identified is non-essential in S. mutans, which is not known in any other bacterium lacking the NIF and/or ISC system. However, how the bacterium compensates the Fe-S deficiency and if any novel Fe-S assembly systems exist in this bacterium await further investigation.

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Finding Ways to Relax: A Revisionistic Analysis of the Chemistry of E. coli GTP Cyclohydrolase II

Biochemistry ◽

10.1021/acs.biochem.1c00511 ◽

2021 ◽

Author(s):

Madison M. Smith ◽

Brett A. Beaupre ◽

Dariush C. Fourozesh ◽

Kathleen M. Meneely ◽

Audrey L. Lamb ◽

...

Keyword(s):

Gtp Cyclohydrolase ◽

E Coli ◽

Gtp Cyclohydrolase Ii

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Cryptococcus neoformans Phosphoinositide-Dependent Kinase 1 (PDK1) Ortholog Is Required for Stress Tolerance and Survival in Murine Phagocytes

Eukaryotic Cell ◽

10.1128/ec.00235-12 ◽

2012 ◽

Vol 12 (1) ◽

pp. 12-22 ◽

Cited By ~ 22

Author(s):

Yeissa Chabrier-Roselló ◽

Kimberly J. Gerik ◽

Kristy Koselny ◽

Louis DiDone ◽

Jennifer K. Lodge ◽

...

Keyword(s):

Cell Wall ◽

Stress Tolerance ◽

Cryptococcus Neoformans ◽

Nitrosative Stress ◽

Galleria Mellonella ◽

Mapk Pathway ◽

Mitogen Activated Protein Kinase ◽

Oxidative And Nitrosative Stress ◽

Independent Manner ◽

Content Type

ABSTRACTCryptococcus neoformansPKH2-01andPKH2-02are orthologous to mammalian PDK1 kinase genes. Although orthologs of these kinases have been extensively studied inS. cerevisiae, little is known about their function in pathogenic fungi. In this study, we show thatPKH2-02but notPKH2-01is required forC. neoformansto tolerate cell wall, oxidative, nitrosative, and antifungal drug stress. Deletion ofPKH2-02leads to decreased basal levels of Pkc1 activity and, consequently, reduced activation of the cell wall integrity mitogen-activated protein kinase (MAPK) pathway in response to cell wall, oxidative, and nitrosative stress.PKH2-02function also is required for tolerance of fluconazole and amphotericin B, two important drugs for the treatment of cryptococcosis. Furthermore, OSU-03012, an inhibitor of human PDK1, is synergistic and fungicidal in combination with fluconazole. Using aGalleria mellonellamodel of low-temperature cryptococcosis, we found thatPKH2-02is also required for virulence in a temperature-independent manner. Consistent with the hypersensitivity of thepkh2-02Δ mutant to oxidative and nitrosative stress, this mutant shows decreased survival in murine phagocytes compared to that of wild-type (WT) cells. In addition, we show that deletion ofPKH2-02affects the interaction betweenC. neoformansand phagocytes by decreasing its ability to suppress production of tumor necrosis factor alpha (TNF-α) and reactive oxygen species. Taken together, our studies demonstrate that Pkh2-02-mediated signaling inC. neoformansis crucial for stress tolerance, host-pathogen interactions, and both temperature-dependent and -independent virulence.

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