Journal
PLANT AND CELL PHYSIOLOGY
Volume 47, Issue 9, Pages 1251-1261Publisher
OXFORD UNIV PRESS
DOI: 10.1093/pcp/pcj095
Keywords
cyanobacteriochrome; GAF domain; photoreceptor; phototaxis; phycocyanobilin; phytochrome
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A putative photoreceptor gene, TepixJ, of a thermophilic cyanobacterium is homologous to SypixJ1 that mediates positive phototaxis in the unicellular motile cyanobacterium Synechocystis sp. PCC 6803. The putative chromophore-binding GAF domain of TePixJ protein was overexpressed as a fusion with a polyhistidine tag (His-TePixJ_GAF) in Synechocystis cells and isolated to homogeneity. The photoreversible conversion of His-TePixJ_GAF showed peaks at 531, 341 and 266 nm for the green light-absorbing form (Pg form), and peaks at 433 and 287 nm for the blue light-absorbing form (Pb form). At 77K, the Pg form fluoresced at 580 nm, while the Pb form did not emit any fluorescence. Mass spectrometry of the tryptic chromopeptide demonstrated that a phycocyanobilin isomer binds to the conserved cysteine at ring A via a thioether bond. It is established that TePixJ and SyPixJ1 are novel photoreceptors in cyanobacteria ('cyanobacteriochromes') that are similar, but distinct from the phytochromes and bacteriophytochromes.
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