Cyanobacteriochrome CcaS is the green light receptor that induces the expression of phycobilisome linker protein

doi:10.1073/pnas.0801826105

Cyanobacteriochrome CcaS is the green light receptor that induces the expression of phycobilisome linker protein

*Department of Life Sciences (Biology), University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan;
^†Life Science Research Center, Shimadzu Corporation, 3-1 Kanda-Nishikicho, Chiyoda-ku, Tokyo 108-8639, Japan; and
^‡College of Industrial Technology, Nihon University, 1-2-1 Izumicho, Narashino, Chiba 275-8575, Japan

Edited by J. Clark Lagarias, University of California, Davis, CA, and approved May 8, 2008 (received for review February 28, 2008)

Abstract

Cyanobacteriochromes are a newly recognized group of photoreceptors that are distinct relatives of phytochromes but are found only in cyanobacteria. A putative cyanobacteriochrome, CcaS, is known to chromatically regulate the expression of the phycobilisome linker gene (cpcG2) in Synechocystis sp. PCC 6803. In this study, we isolated the chromophore-binding domain of CcaS from Synechocystis as well as from phycocyanobilin-producing Escherichia coli. Both preparations showed the same reversible photoconversion between a green-absorbing form (Pg, λ_max = 535 nm) and a red-absorbing form (Pr, λ_max = 672 nm). Mass spectrometry and denaturation analyses suggested that Pg and Pr bind phycocyanobilin in a double-bond configuration of C15-Z and C15-E, respectively. Autophosphorylation activity of the histidine kinase domain in nearly full-length CcaS was up-regulated by preirradiation with green light. Similarly, phosphotransfer to the cognate response regulator, CcaR, was higher in Pr than in Pg. From these results, we conclude that CcaS phosphorylates CcaR under green light and induces expression of cpcG2, leading to accumulation of CpcG2-phycobilisome as a chromatic acclimation system. CcaS is the first recognized green light receptor in the expanded phytochrome superfamily, which includes phytochromes and cyanobacteriochromes.

Footnotes

^§To whom correspondence should be addressed. E-mail: mikeuchi{at}bio.c.u-tokyo.ac.jp
Author contributions: Y.H. and M.I. designed research; Y.H., T.S., R.N., and M.K. performed research; Y.H. and T.S. analyzed data; and Y.H. and M.I. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
The sequences reported in this paper have been deposited in Cyanobase or GenBank [accession nos. sll1473–5, ABI83649 (SyCcaS), slr0473, Q55168 (Cph1), ZP_00106627 (NpCcaS), AAB08575 (FdRcaE), NP_285374 (DrBphP), and NP_948356 (RpBphP3)].
This article contains supporting information online at www.pnas.org/cgi/content/full/0801826105/DCSupplemental.