The SRP and the nascent polypeptide chain–ribosome complex bind to the SRP receptor in the ER membrane. This interaction is strengthened by the binding of GTP to both the SRP and its receptor.

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Phototropin receptors are associated with the plasma membrane, where they function as light-activated serine/threonine kinases.

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#Id: 9859

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Phototropin contains two light-sensing LIGHT-OXYGEN-VOLTAGE (LOV) domains, LOV1 and LOV2, each binding a chromophore flavin mononucleotide (FMN).

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In the dark, the maximum absorption of the FMN chromophore is around 450 nm. 

Blue light induces the formation of a covalent bond between FMN and a cysteine residue, shifting the absorption maximum to 390 nm via a LOV660 intermediate form. The reaction is reversible in darkness.

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LOV2 domain is essential for blue light–induced kinase activation and autophosphorylation of the phototropin photoreceptor.

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#Id: 9862

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#Id: 9863

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