Part:BBa_K4601010
NpSRII-NpHtrII-EnvZ
This part is a fusion protein between the Natronomonas pharaonis NpSRII sensory rhodopsin (BBa_K4601005), the NpHtrII transmembrane domain and the E. coli EnvZ histidine kinase domain.
Usage and Biology
Sensory rhodopsins are not pumps, but photoreceptors that respond to light and transmit the signal into the cell via a signaling cascade. For this, in N. pharaonis, NpSRI and NpSRII interact with the transducer proteins NpHtrI and NpHtrII, respectively [1]. NpHtrI and NpHtrII are homodimeric membrane proteins that have also a cytoplasmic histidine kinase domain responsible for initiating the signaling cascade that mediates chemotaxis. The interaction between the SR and their cognate Htr transducers are highly specific.
Halorhodopsins are chloride inward pumps activated by light [2]. To detect this activity in E. coli we designed a halorhodopsin screening system that uses fusion proteins composed of the halorhodopsin of interest, the NpHtrII transmembrane domain and the E. coli EnvZ histidine kinase domain. This design is based on several considerations:
-> The HR is covalently linked to the NpHtrII transmembrane domain (via a short linker sequence) to ensure their colocalization
-> The natural histidine kinase domain of the NpHtrII was removed as it does not specifically interact with an E. coli signaling cascade. It was replaced by an endogenous E. coli histidine kinase domain.
-> The E. coli EnvZ was chosen as a histidine kinase domain as it is part of the widely known EnvZ-OmpR two component system [3].
In this system (Figure 1), it is expected that in the presence of light the halorhodopsin activation is transmitted via protein-protein interaction to the NpHtrII transmembrane domain, which in turn leads to the autophosphorylation of the EnvZ histidine kinase domain and subsequently the phosphorylation of the OmpR transcription factor. The phosphorylated OmpR dimerises and binds to specific sequences present in the promoter regions of the ompC and ompF genes thus upregulating their expression.
Based on this property, we designed several reporters in which the pOmpC promoter controls the expression of sfGFP (BBa_K4601223), LacZ𝛼 ((BBa_K4601233), the ampicillin resistance gene AmpR (BBa_K4601243) or chloramphenicol resistance gene CmR (BBa_K4601253).
Opsin activation should lead to the expression of the reporter gene and the detection of either a fluorescent output, a colorimetric one, or the capacity to grow in the presence of ampicillin or chloramphenicol. The latter systems would constitute a good selection tool for the identification of halorhodopsins with improved properties in different conditions of light.
To be functional in E. coli this system requires the knockout of the natural envZ' gene.
Figure 1: Design of the halorhodopsin activity detection system based on fusion proteins and the E. coli EnvZ/OmpR two component system.
For the characterisation of this part an expression cassette was assembled and the results are presented on its page in Parts Registry: BBa_K4601210.
References
[1] Jung KH, Spudich EN, Trivedi VD, Spudich JL. An archaeal photosignal-transducing module mediates phototaxis in Escherichia coli. Journal of Bacteriology (2001) 183: 6365–6371.
[2] Engelhard C, Chizhov I, Siebert F, Engelhard M. Microbial halorhodopsins: light-driven chloride pumps. Chemical Reviews (2018) 118: 10629–10645.
[3] Mizuno T, Mizushima S. Signal transduction and gene regulation through the phosphorylation of two regulatory components: the molecular basis for the osmotic regulation of the porin genes. Molecular Microbiology (1990) 4: 1077–1082.
Sequence and Features
- 10COMPATIBLE WITH RFC[10]
- 12COMPATIBLE WITH RFC[12]
- 21COMPATIBLE WITH RFC[21]
- 23COMPATIBLE WITH RFC[23]
- 25INCOMPATIBLE WITH RFC[25]Illegal NgoMIV site found at 73
Illegal NgoMIV site found at 331 - 1000INCOMPATIBLE WITH RFC[1000]Illegal SapI site found at 801
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