Source Sensory Rhodopsin II and HtrII domains were taken from the genome of Natronomonas Pharaonis. The Tar methyl accepting chemotaxis protein was taken from Salmonella Enterica Serovar Typhimurium. The synthetic linker and fusing of the HAMP domains of HtrII and StTar was done by the team behind the referenced article (1).
Molecular mechanism of the photosensor The fusion,chimera-protein coupled to the chemotaxis pathway. Figure taken from Trivedi et al.(2) The fusion,chimera-protein coupled to the chemotaxis pathway. Figure taken from Trivedi et al.(2) The photosensor acts directly on the tumbling frequency by effecting E. Coli's normal chemotaxis pathway. When exposed to bluelight, the sensory rhodopsin II will absorb the photons and undergo a change in ultrastructure, which is being transduced through HtrII on to the Tar domain. This effects decreases the autophosphorylation of the CheA protein, which in turn again decreases the amount of phosphorylated CheY, which just means that less of it will get phosphorylated. If there is less of the CheY-P, then there is a smaller chance of one of these molecules binding to the flagellar motor and making it turn clockwise, thereby inducing a lowered tumbling frequency in the system. The photosensor can also act in the opposite way, inducing a higher tumbling rate in the bacteria. Which effect the sensor will have depends on where NpHtrII and StTar are fused in the HAMP domain. If the fusion contains 20 more basepair of the HtrII domain and 20 less of the Tar domain, the photosensor would have the opposite effect and would be increasing the autophosphorylation of CheA. Usage and parameters The part requires retinal to work in E.Coli. This can be achieved through adding retinal to the liquid growth medium and/or the plates. Currently we are doing experiments on wether the part also functions with an internal retinal source, ie retinal synthesis in E. Coli. On top of adding retinal the cells will have to be grown in the dark for at least two hours after the addition of retinal to the growth medium if you want to see an effect. This is so that the photosensor is not exposed to light before the experiments and will result in maximum output if exposed to blue light. Results Bacteria containing this part will exhibit a lowered tumbling rate when exposed to blue light (wavelengths around 350nm - 450nm). This was analysed with the help of video microscopy and the open source software "CellTrack". The individual cells trajectory was tracked and their speed measured. The tracking results are as follows: From left to right, trajectory of: E.Coli with photosensor exposed to blue light, E.Coli with photosensor exposed to red light and E.Coli Mg1655 Wildtype exposed to blue light: (Blue dots show the location of the cell in the given frame, so the number of dots equals the number of frames from the sample.) The phototaxic bacteria move more in a straight line when exposed to bluelight, as can be seen when comparing the trajectories of the thee bacteria given earlier. These were taken from a batch of 10 cells tracked per sample.
Design Notes NpSopII-NpHtrII-StTar fusion-chimera protein sequence from Jung K-H, Spudich EN, Trivedi VD and Spudich JL (1). The first 224 amino acid residues come from the NpSopII gene, encoding a bluelight photon receptor with 15 residues removed at the C-terminal end. The following 9 amino acids are a linker. the last part is HtrII fused with Tsr from E.Coli at the HAMP domain. The complex' first 125 amino acid residues come from HtrII and the remaining 279 from Tsr. The constitutive promoter R0040 was chosen for its medium strength, so that there would be a rather large amount of the fusion, chimera protein expressed, but not so much that it would be lethal to the cell. The easy repression and inhibition of repression through TetR and tetracycline makes for an easily controlled expression if that is needed. The doible terminator B0015 was chosen for it's reliability and good reviews on the partsregistry.
Double terminator consisting of BBa_B0010 and BBa_B0012
RBS (Elowitz 1999) -- defines RBS efficiency
Varies from -6 to +1 region from original sequence to accomodate BioBricks suffix. No secondary structures are formed in the given RBS region. Users should check for secondary structures induced in the RBS by upstream and downstream elements in the +50 to -50 region, as such structures will greatly affect the strength of the RBS. Contact info for this part: Brian Chow
Vinay S Mahajan, Voichita D. Marinescu, Brian Chow, Alexander D Wissner-Gross and Peter Carr IAP, 2003.
Derived from the TE terminator of T7 bacteriophage between Genes 1.3 and 1.4 <genbank>V01146</genbank>.
Transcription terminator for the E.coli RNA polymerase.
Suggested by Sri Kosuri and Drew Endy as a high efficiency terminator. The 5' end cutoff was placed immediately after the TAA stop codon and the 3' end cutoff was placed just prior to the RBS of Gene 1.4 (before AAGGAG). Use anywhere transcription should be stopped when the gene of interest is upstream of this terminator.
Transcriptional terminator consisting of a 64 bp stem-loop.
Lutz, R., Bujard, H., Nucleic Acids Research (1997) 25, 1203-1210.
Sequence for pTet inverting regulator driven by the TetR protein.
BBa_R0040 TetR-Regulated Promoter is based on a cI promoter. It has been modified to include two TetR binding sites and the BioBrick standard assembly head and tail restriction sites.
June Rhee, Connie Tao, Ty Thomson, Louis Waldman
Conversion of the iGEM parts registry to SBOL2.1