S-Space College of Natural Sciences (자연과학대학) Dept. of Biological Sciences (생명과학부) Theses (Ph.D. / Sc.D._생명과학부)
Regulation and Function of Redox Sensor SoxR in Streptomyces coelicolor
Streptomyces coelicolor에서 산화환원 센서인 SoxR의 기능과 조절
- Jung-Hye Roe
- 자연과학대학 생명과학부
- Issue Date
- 서울대학교 대학원
- Molecular Microbiology; SoxR; Fe-S; redox-active compounds; EPR; redox potential; oxidative stress; superoxide
- 학위논문 (박사)-- 서울대학교 대학원 : 생명과학부, 2014. 8. Jung-Hye Roe.
- Redox-sensitive transcription factor SoxR in enteric bacteria regulates cellular response toward superoxide and nitric oxide via inducing the expression of a downstream regulator SoxS, that activates more than 100 genes. In other bacterial groups, however, SoxR directly induces its multiple target genes in response to redox-active compounds, as initially demonstrated for psuedomonads. The antibiotic-producing soil bacterium Streptomyces coelicolor contains a gene for SoxR homologue (SCO1697) whose DNA-recognition helix is identical to that of Escherichia coli SoxR. Using E. coli SoxR binding sequence, five candidate genes of SoxR reglulon were predicted. It was demonstrated that SoxR binds to their promoter regions and activates their expression concurrently with the production of blue polyketide antibiotic actinorhodin (a benzoisochromanequinone). These genes encode probable NADPH-dependent flavin reductase (SCO2478), NADPH-dependent quinone reductase (SCO4266), ABC-transporter (SCO7008), monooxygenase (SCO1909), and a hypothetical protein (SCO1178). Addition of actinorhodin to exponentially growing cells activated the expression of SoxR target genes in a SoxR-dependent manner.
SoxR from E. coli and related enterobacteria is activated by a broad range of redox-active compounds through oxidation or nitrosylation of its [2Fe-2S] cluster. In contrast, non-enteric SoxRs appear to get activated by a narrower range of redox-active compounds that include endogenously produced metabolites. The responsiveness of SoxRs from Streptomyces coelicolor (ScSoxR), Pseudomonas aeruginosa (PaSoxR) and E. coli (EcSoxR), all expressed in S. coelicolor, were compared toward natural or synthetic redox-active
compounds. EcSoxR responded to all compounds examined, whereas ScSoxR was insensitive to oxidants such as paraquat (Eh -440 mV) and menadione sodium bisulfite (Eh -45 mV) and to nitric oxide (NO) generators. PaSoxR was insensitive only to some NO generators. Whole cell EPR analysis of SoxRs expressed in E. coli revealed that the [2Fe-2S]1+ of ScSoxR was not oxidizable by paraquat, differing from EcSoxR and PaSoxR. The mid-point redox potential of purified ScSoxR was determined to be -185 ± 10 mV, higher by ~100 mV than those of EcSoxR and PaSoxR, coinciding with its insensitivity to paraquat. The overall sensitivity profile indicates that both redox potential and kinetic reactivity determine the differential responses of SoxRs toward various oxidants. Residues within the [2Fe-2S] binding site, which are specific to ScSoxR, were mutated and were evaluated for their effects on the sensitivity profile.
Streptomyces coelicolor, SoxR, Fe-S, redox-active compounds, EPR, redox potential, oxidative stress, superoxide