Cyanobacteriochrome CcaS is Novel Green/Red Light Receptor that Carries Phycocyanobilin and Induces the Expression of Phycobilisome Linker Protein by Green Light

Abstract

A cyanobacteriochrome CcaS is known to regulate the expression of phycobilisome linker gene (cpcG2) in Synechocystis sp. PCC 6803. We previously reported that CcaS shows the reversible photoconversion between a green-absorbing form (Pg) and a red-absorbing form (Pr). In this study, mass spectrometry and denaturation analysis revealed that CcaS binds PCB in a configuration of ZZZ and ZZE for Pg and Pr, respectively. Autophosphorylation of histidine kinase of nearly full-length CcaS was up-regulated by preillumination with green light. Similarly, phosphotransfer to the cognate response regulator CcaR was higher in the Pr form than Pg. From these results, we concluded that green-light activated phosphorylation from CcaS to CcaR induces the expression of cpcG2, leading to accumulate CpcG2-phycobilisome. We will discuss about the universality of the CcaS system, which is also found in Nostoc punctiforme PCC 73102.