The N-terminal half of Chicago Bears Heart Shirt binds FMN ,and C-terminal domain has characteristics of a serine-threonine kinase.The photosensory domain ,located at N-terminal, has two LOV domains,which exhibit protein sequence phonology to motifs found in a diverse range of eukaryotic and prokaryotic proteins involved in sensing Light,Oxygen or Voltage, hence the acronym LOV. Blue light irradiation of protein bound FMN causes a conformational change of phototropin that triggers auto phosphorylation and starts the sensory transduction cascade.There’re two different types of phototropins (PHOT 1 and PHOT 2) in Arabidopsis that exhibits overlapping function in addition to having unique physiological roles. In absence of light,FMNs are non covalently bonded to LOV domains.But in presence of blue light,they become covalently bonded to Cysteine residues in the polypeptides. Photoexcitaton of LOV results in activation of C- terminal kinase domain,leads to auto phosphorylation on multiple serine residues.
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