Photosensitive proteins are a kind of protein molecules that can change their structure after receiving light stimulation of a specific wavelength. Photosensitive proteins exist in many organisms in nature, which enable organisms to respond to changes in environmental light. Some photosensitive proteins will undergo heterodimerization with another protein after being stimulated by light at a specific wavelength, while some photosensitive proteins will undergo homo dimerization or Homo oligomerization. These two types of photo-regulated protein-protein interactions are widely used in photogenetic technology to control various cell behaviors. The three widely used photosensitive proteins are phytochrome, cryptochrome and light oxygen voltage sensing domain.
Photosensitive protein is the core of photogenetics technology and its application. Several common photosensitive proteins have their own advantages and disadvantages.
The advantage of phyB is that its activation light is red light, which has less toxicity to cells and can penetrate tissues more effectively; However, animal cells lack the cofactor PCB required for the action of phyB, so the use of phyB in animal cells requires the addition of exogenous PCB or additional synthesis in animal cells.
In addition, the phyB protein molecule (908 amino acids) is relatively large, which may affect the function of the fusion protein.
In contrast, CRY2 has a slightly smaller molecular weight (498 amino acids), and the required cofactor fad exists in most animal cells without additional cofactors. However, the blue light required for CRY2 activation is toxic to cells, and the tissue penetration is weak. In addition, CRY2 is unique in that the photosensitive protein can carry out two different protein-protein interactions at the same time; Homodimerization and heterodimerization. Therefore, CRY2 is the best choice if some optogenetic applications need to use both types of interactions at the same time. On the other hand, the uniqueness will become a disadvantage; If some optogenetic applications only require heterodimerization, the simultaneous homodimerization of CRY2 may introduce side effects and affect the final results. At the same time, the molecular weight of the polymer produced by the homologous polymerization of CRY2 is difficult to be consistent, so the use of CRY2 may become complex.
Lov domain has unique light induced conformational changes. A single lov domain can not only cooperate with other functional proteins to complete photobraking, but also produce homologous dimerization through modification. The properties, advantages and disadvantages of each photosensitive protein are different. Different optogenetic applications require different light response behaviors. For example, some applications need to be quickly started and closed to achieve high time accuracy, some applications need to achieve high spatial accuracy locally in cells, and some applications need strong homologous and heterodimerization reactions at the same time.
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