Melbourne/Blue Photosensor

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As part of the overall system design. A blue light sensitive pathway is required in addition to the red light sensitive pathway. Described below is the blue photosensor. This involves the design of a chimeric trans-membrane protein. A blue light sensitive (~500nm) integral photo receptor SopII that dimerizes with a histidine kinase; HtrII (As described in 2001 paper).

This will be fused to a two-component system from Bacillus subtilis - so as to not affect any endogenous networks. The two component system involves: comP - two-component sensor histidine kinase, comA - two-component response regulator. Phosphorylated comA will upregulated transcription via srfA promoter (link required), as part of the AND gate.

Contents

Blue Photosensor Background

Method

Possible extensions:

  • Determination of optimal wavelength:
    • use of different substrates (different retinals)
  • Separate variants all submitted as BioBricks.
  • Submitted synthesized ComP and ComA as BioBricks
  • Model the pathway to determine rate-limiting step

References

This part is based on “Photostimulation of a Sensory Rhodopsin II/HtrII/Tsr Fusion Chimera Activates CheA-Autophosphorylation and CheY-Phosphotransfer in Vitro” by Vishwa D. Trivedi and John L. Spudich, Biochemistry 2003, 42, 13887-13892. Acording to this article the peak sensitivity is to 500+/-5nm, and results in a 3 fold activation of the Tsr.. CheA,W,Y connected system.

It is proposed to replace Tsr with homolgouse ComP. SRII-HtrII fusion to which ComP is fused CopA when phosphorylated by ComP is an activator for PsfA promoter sequence from Dr Alan Grossman (M.I.T.) Based on

  • SRII-HtrII-Tsr fusion from Prof J.L. Spudich (university of Texas)melb:spudich N sequence
  • BBa_J51000 (ComP) kinase
  • BBa_J51001 (ComA) activator

PARTS:

  • SrfA promoter
  • ComA protein generator
  • SRII-ComP photosensor
  • Any phyco construction genes?

SRII is from Natronomonas pharaonis.

Tsr fusion was made by Jung et al J Bacteriol 183 6365-6371 (2001) they propose a mechanism. I don’t see why anyone thinks this will work!!! Currently a conformational change induced by light increases affinity in TSR for Che family which leads to cross phosphorylation. To replace TSR with a kinase would require the kinase activity to be modulated – hence matching using homology as was done for tsr is not likely to work. Also what are the normal functions of ComP etc.