Reactive sulfur species sensor
SqrR is a repressor protein that is involved in sulfide-dependent gene expression in the bacterium Rhodobacter capsulatus. 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). 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.
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. When RSS are present, reaction with SqrR induces the expression of the reporter gene. The part consists of the fluorescent reporter gene CreiLov placed under control of the Psqr promoter, sqrR, the gene that encodes SqrR, placed under control of a constitutive promoter, as well as biobrick ribosomal binding sites and terminators.
Note: In order to function as a hydrogen sulfide sensor, the part must be used in conjugation with a component that oxidises sulfide to S0, such as SQR. In our project, oxidised glutathione (GSSG) was reacted with sulfide to form glutathione persulfide (GSSH), a RSS.
 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
- 10Illegal PstI site found at 214
- 12Illegal NheI site found at 536
Illegal NheI site found at 559
Illegal PstI site found at 214
- 21Illegal XhoI site found at 491
Illegal XhoI site found at 835
- 23Illegal PstI site found at 214
- 25Illegal PstI site found at 214
- 1000COMPATIBLE WITH RFC