Essential role of the A'?/A? gap in the N-terminal upstream of LOV2 for the blue light signaling from LOV2 to kinase in Arabidopsis photototropin1, a plant blue light receptor.

ABSTRACT: Phototropin (phot) is a blue light (BL) receptor in plants and is involved in phototropism, chloroplast movement, stomata opening, etc. A phot molecule has two photo-receptive domains named LOV (Light-Oxygen-Voltage) 1 and 2 in its N-terminal region and a serine/threonine kinase (STK) in its C-terminal region. STK activity is regulated mainly by LOV2, which has a cyclic photoreaction, including the transient formation of a flavin mononucleotide (FMN)-cysteinyl adduct (S390). One of the key events for the propagation of the BL signal from LOV2 to STK is conformational changes in a J?-helix residing downstream of the LOV2 C-terminus. In contrast, we focused on the role of the A'?-helix, which is located upstream of the LOV2 N-terminus and interacts with the J?-helix. Using LOV2-STK polypeptides from Arabidopsis thaliana phot1, we found that truncation of the A'?-helix and amino acid substitutions at Glu474 and Lys475 in the gap between the A'? and the A? strand of LOV2 (A'?/A? gap) to Ala impaired the BL-induced activation of the STK, although they did not affect S390 formation. Trypsin digested the LOV2-STK at Lys603 and Lys475 in a light-dependent manner indicating BL-induced structural changes in both the J?-helix and the gap. The digestion at Lys603 is faster than at Lys475. These BL-induced structural changes were observed with the Glu474Ala and the Lys475Ala substitutes, indicating that the BL signal reached the J?-helix as well as the A'?/A? gap but could not activate STK. The amino acid residues, Glu474 and Lys475, in the gap are conserved among the phots of higher plants and may act as a joint to connect the structural changes in the J?-helix with the activation of STK.

SUBMITTER: Kashojiya S 

PROVIDER: S-EPMC4401697 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature