Specific Interaction Between CpcG2-Phycobilisome and Photosystem I

Abstract

Previously, we reported that the uni-cellular cyanobacterium Synechocystis sp. PCC 6803 possesses two types of phycobilisome which differ in their interconnecting " rod-core linker " proteins (CpcG1 and CpcG2). We showed that CpcG2 forms a unique variant phycobilisome (CpcG2-PBS), which is composed of phycocyanin rods and CpcG2 but devoid of core allophyco-cyanins (Kondo et al. 2005). We also reported that CpcG2-PBS is associated with the thylakoid membrane more tightly than CpcG1-PBS, and that it is engaged in preferential energy transfer to photosystem I (Kondo et al. 2007). Here, we fractionated thylakoid membranes by β-dodecyl-maltoside-glycerol density gradient centrifugation containing sodium cholate. A part of CpcG2 was copurified with PSI trimer, while no CpcG1 was copurified with it. It is suggested that the CpcG2-PBS interacts with photosystem I trimers more stably than the CpcG1-PBS.