Spectral properties of bacteriophytochrome AM1_5894 in the chlorophyll d-containing cyanobacterium Acaryochloris marina

• Published in: Scientific reports Vol. 6; no. 1; p. 27547
• Main Authors: Loughlin, Patrick C., Duxbury, Zane, Mugerwa, Tendo T. Mukasa, Smith, Penelope M. C., Willows, Robert D., Chen, Min
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 10.06.2016; Nature Publishing Group
• Subjects: 631/449; 631/45; 82/29; 82/80; Chlorophyll; Cyanobacteria; Genomes; Humanities and Social Sciences; Kinases; multidisciplinary; Organisms; Photoreceptors; Proteins; Science; Science (multidisciplinary); Signal transduction
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep27547

Acaryochloris marina , a unicellular oxygenic photosynthetic cyanobacterium, has uniquely adapted to far-red light-enriched environments using red-shifted chlorophyll d . To understand red-light use in Acaryochloris , the genome of this cyanobacterium was searched for red/far-red light photoreceptors from the phytochrome family, resulting in identification of a putative bacteriophytochrome AM1_5894 . AM1_5894 contains three standard domains of photosensory components as well as a putative C-terminal signal transduction component consisting of a histidine kinase and receiver domain. The photosensory domains of AM1_5894 autocatalytically assemble with biliverdin in a covalent fashion. This assembled AM1_5894 shows the typical photoreversible conversion of bacterial phytochromes with a ground-state red-light absorbing (Pr) form with λ BV max [Pr] 705 nm, and a red-light inducible far-red light absorbing (Pfr) form with λ BV max [Pfr] 758 nm. Surprisingly, AM1_5894 also autocatalytically assembles with phycocyanobilin, involving photoreversible conversion of λ PCB max [Pr] 682 nm and λ PCB max [Pfr] 734 nm, respectively. Our results suggest phycocyanobilin is also covalently bound to AM1_5894, while mutation of a cysteine residue (Cys11Ser) abolishes this covalent binding. The physiological function of AM1_5894 in cyanobacteria containing red-shifted chlorophylls is discussed.