Channelrhodopsin-2

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Mechanics

Channelrhodopsin-2 consists of a 7-transmembrane helix protein, as in many other rhodopsoins, but ChR2 has a covalently linked retinal. The peak absorbance of the Channelrhodopsin-2 retinal complex is about 460 nm. When the all-trans retinal complex absorbs light, it induces a conformational change, probably to 13-cis-retinal. This conformational change introduces a further conformational change in the transmembrane protein opening the pore, to at least 6A. The 13-cis-retinal naturally relaxes with time back to the all-trans-retinal which closes the pore, stopping the flow of ions.^[1]

The 7-transmembrane nature of Channelrhodopsin-2 is fairly rare to ion channels which usually consist of similar repeating parts.^[1]

Applications

This makes depolarization of excitable cells very fast, robust, and useful for bioengineering and neuroscience applications, called optogenetics, including photostimulation of neurons for probing of neural circuits. Channelrhodopsin-2 and the yellow light-activated chloride pump halorhodopsin together enable multiple-color optical activation and silencing of neural activity. The C-terminal end of ChR2 extends well into the intracelluar space, whereas the N-terminal end consists of the 7-transmembrane section. As such, the C-terminus can be replaced by the green fluorescent protein (GFP).

References

1. ^ ^{a b} "Channelrhodopsin-2, a directly light-gated cation-selective membrane channel" - PNAS | November 25, 2003 | vol. 100 | no. 24 | 13940-13945