A phytochrome-like protein AphC triggers the cAMP signaling induced by far-red light in the cyanobacterium Anabaena sp. strain PCC7120.
In the filamentous, nitrogen-fixing cyanobacterium Anabaena sp. PCC7120, red light (630 nm) decreased, whereas far-red light (720 nm) increased cellular adenosine 3',5'-cyclic monophosphate (cAMP) content. To find a red and far-red light photoreceptor that triggers the cAMP signal cascade, we disrupted 10 open reading frame having putative chromophore-binding GAF domains. The response of the cellular cAMP concentration to red and far-red light in each open reading frame disruptant was determined. It was found that only the mutant of the gene all2699 failed to respond to far-red light. The open reading frame named as aphC encoded a protein with 920 amino acids including GAF domains similar to those involved in Cph2, a photoreceptor of Synechocystis sp. PCC6803. To determine which adenylate cyclase (AC) is responsible for far-red light signal, we disrupted all AC genes and found that CyaC was the candidate. The enzymatic activity of CyaC might be controlled by a far-red light photoreceptor through the phosphotransfer reaction. The site-specific mutant of the Asp59 residue of the receiver (R1) domain of CyaC lost its light-response capability. It was suggested that the far-red light signal was received by AphC and then transferred to the N-terminal response regulator domain of CyaC. Then its catalytic activity was stimulated, which increased the cellular cAMP concentration and drove the subsequent signal transduction cascade.
Okamoto
Shinobu
S
Department of Biology, Graduate School of Arts and Sciences, University of Tokyo, Tokyo, Japan.
Kasahara
Masahiro
M
Kamiya
Asako
A
Nakahira
Yuka
Y
Ohmori
Masayuki
M
D000262:Adenylyl Cyclases / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D017033:Anabaena / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D003116:Color; D000242:Cyclic AMP / Q000378:metabolism*; D008027:Light; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010834:Phytochrome / Q000737:chemistry / Q000378:metabolism*; D017354:Point Mutation / Q000235:genetics; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000528:radiation effects*; D040681:Structural Homology, Protein
D001426:Bacterial Proteins; D010834:Phytochrome; D000242:Cyclic AMP; D000262:Adenylyl Cyclases