期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 110, 期 13, 页码 4974-4979出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1302909110
关键词
light sensing; phycobiliprotein; signal transduction; spectral tuning; two-component signaling
资金
- Japanese Society for the Promotion of Science [23370014, 09J09146]
- Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy [DOE DE-FG02-09ER16117]
- Grants-in-Aid for Scientific Research [23370014, 09J09146, 25620028] Funding Source: KAKEN
Cyanobacteriochromes (CBCRs) are cyanobacterial members of the phytochrome superfamily of photosensors. Like phytochromes, CBCRs convert between two photostates by photoisomerization of a covalently bound linear tetrapyrrole (bilin) chromophore. Although phytochromes are red/far-red sensors, CBCRs exhibit diverse photocycles spanning the visible spectrum and the near-UV (330-680 nm). Two CBCR subfamilies detect near-UV to blue light (330-450 nm) via a two-Cys photocycle that couples bilin 15Z/15E photoisomerization with formation or elimination of a second bilin-cysteine adduct. On the other hand, mechanisms for tuning the absorption between the green and red regions of the spectrum have not been elucidated as of yet. CcaS and RcaE are members of a CBCR subfamily that regulates complementary chromatic acclimation, in which cyanobacteria optimize light-harvesting antennae in response to green or red ambient light. CcaS has been shown to undergo a green/red photocycle: reversible photoconversion between a green-absorbing 15Z state (P-15Z(g)) and a red-absorbing 15E state (P-15E(r)). We demonstrate that RcaE from Fremyella diplosiphon undergoes the same photocycle and exhibits light-regulated kinase activity. In both RcaE and CcaS, the bilin chromophore is deprotonated as P-15Z(g) but protonated as P-15E(r). This change of bilin protonation state is modulated by three key residues that are conserved in green/red CBCRs. We therefore designate the photocycle of green/red CBCRs a protochromic photocycle, in which the dramatic change from green to red absorption is not induced by initial bilin photoisomerization but by a subsequent change in bilin protonation state.
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