Part:BBa_K3762008

Sulfide sensor

SqrR is a repressor protein that is involved in sulfide-dependent gene expression in the bacterium Rhodobacter capsulatus.[1] When no sulfide is present, SqrR binds to the Psqr promoter, inhibiting the expression of the gene encoding Sulfide:quinone oxidoreductase (SQR). SQR is an enzyme that oxidises sulfide to zero-valent sulfur (S0), which can then conjugate with multiple different nucleophiles or low molecular weight thiols to form reactive sulfur species (RSS).[1] Upon reaction with a RSS, a di-, tri-, or tetrasulfide bond forms between two cysteine residues of SqrR, resulting in a conformational change that reduces its DNA binding affinity. RSS thereby functions as inducers of the genes under control of the Psqr promoter that is repressed by SqrR.[1]

This composite part takes advantage of the sulfide-binding properties of SqrR, as well as its repressor function, so as to function as a sensor for hydrogen sulfide. The part consists of the fluorescent reporter gene CreiLov placed under control of the Psqr promoter, sqr, the gene that encodes SQR, placed under control of a constitutive promoter, sqrR, the gene that encodes SqrR, placed under control of a constitutive promoter, as well as biobrick ribosomal binding sites and terminators.

When hydrogen sulfide diffuses across the cell membrane, the constitutively expressed SQR oxidises sulfide to S0. The oxidized S0 can then react with SqrR, inducing the expression of the reporter protein.

[1] Shimizu, T., Shen, J., Fang, M., Zhang, Y., Hori, K., Trinidad, J. C., Bauer, C. E., Giedroc, D. P., & Masuda, S. (2017). Sulfide-responsive transcriptional repressor SqrR functions as a master regulator of sulfide-dependent photosynthesis. Proceedings of the National Academy of Sciences of the United States of America, 114(9), 2355–2360. https://doi.org/10.1073/pnas.1614133114

Sequence and Features

Assembly Compatibility:

• 10
  INCOMPATIBLE WITH RFC[10]

  Illegal PstI site found at 211
  
• 12
  INCOMPATIBLE WITH RFC[12]

  Illegal NheI site found at 537
  Illegal NheI site found at 560
  Illegal NheI site found at 1980
  Illegal NheI site found at 2003
  Illegal PstI site found at 211
  
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal XhoI site found at 2279
  
• 23
  INCOMPATIBLE WITH RFC[23]

  Illegal PstI site found at 211
  
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal PstI site found at 211
  
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal BsaI site found at 865