Biochemical analysis of the light regulation mechanism of the kinase by LOV2 domain in Arabidopsis Phototropin 1

Abstract

Phototropins (Phot) are one of the important blue light receptors in plants and are involved in phototropism, stomata opening and chloroplast relocation. The N-terminal half has two light-receptive domains (LOV1, LOV2) each of which binds an FMN and the C-terminal half forms a Ser/Thr kinase (KD) connected to the LOV2 with a linker. The kinase activity is inhibited by LOV2 in the dark. Blue light cancels the inhibition, resulting in both auto- and substrate phosphorylation. But little is known about the light regulation mechanism of the kinase by LOV2.
Bacterially expressed Arabidopsis Phot1 LOV2-KD showed the same spectral changes (dark recovery t_1/2 = 29 s) as that of the LOV2 on blue light. The limited proteolysis indicated that light-induced structural changes occurred in the linker. LOV2-KD also showed kinase activity on the peptide of Phot1-N-terminal region. How the light-induced conformational changes regulate the kinase activity of Phot1 will be discussed.