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KillerRed is a key protein in our bacterial density control system. It represents the light-sensitive element that allows the cells to receive signals from the control device.
KillerRed is a red fluorescent protein, meaning that by illuminating it with wavelengths from a certain portion of the visible spectrum, it re-emits light in another portion with longer (less energetic) wavelengths. Below is the absorption and emission spectra for the KillerRed protein:
The KillerRed protein absorption (left peak) and emission (right peak) spectra
Source:Detailed KillerRed description from Evrogen
Below is a comparison of the 3D structures of monomeric dsRed and KillerRed:
KillerRed is a 240 amino acid protein with a 3D structure similar to other fluorescent proteins, with an eleven-strand beta-barrel surrounding an alpha-helix containing the chromophore, source of the protein's optical properties.
KillerRed has a DsRed-type chromophore formed with residues 67Q (glutamine), 68Y (tyrosine), and 69G (glycine), to make QYG. The corresponding coding sequence can be found at the code segment CAGTACGGC.
The interesting properties of the protein are directly related to a unique structural difference among fluorescent proteins, consisting in an open channel linking the chromophore to the environment outside the protein. According to litterature, this is the reason KillerRed is able to produce 1000-fold more reactive oxygen species compared to EGFP which is another ROS-producing fluorescent protein.
KR was originally engineered from the anm2CP anthomedusa chromoprotein by individual amino acid mutations in order to obtain fluorescence and an open channel linking the chromophore to the environment.
