Identification of biochemical association of phycobilisome with photosystems in cyanobacterial state transition

Abstract

State transition is a short-term balance mechanism of energy distribution between photosystem II (PSII) and PSI. Although light-induced state transition in cyanobacteria has been suggested to depend completely on the phycobilisome (PBS) movement between PSII and PSI, the biochemical evidence has not been clearly shown. In this study, we locked the association of PBS with PSII or PSI using glycinebetaine when cells attain State 1 or 2 by exposure to light of blue or green, respectively. Subsequently, the PBS-reaction centers were resolved by blue native polyacrylamide gel electrophoresis and two-dimensional electrophoresis, and then identified by western blot analysis. The results showed that in wild-type (WT) Synechocystis sp. strain PCC 6803, the PBS core always co-migrates with the PSII dimer during light-induced State 1 -State 2 transition, but its rod leaves the PSII dimer in State 2 regardless of its co-migration in State 1. In the light-induced State 2, the co-migration of PBS rod with PSI trimer was observed in WT, but not in DndhB (M55), a State-2-transition-deficient mutant. This study first provided the biochemical evidence for the association of PBS with photosystems during cyanobacterial state transition.

Revisiting cyanobacterial state transitions

“…The possible diffusion of PBS along the thylakoid membrane was first showed by fluorescence recovery after photobleaching (FRAP) experiments in Dactylococcopsis salina and S. elongatus, showing that PBS-photosystem association is a dynamic process which depends on weak interactions with membrane lipids. 86,87 Based on FRAP experiments and to the possible association of PBSs with PSI and PSII, 57,82,94 the hypothesis of a light-harvesting complex moving and modulating the energy reaching each photosystem, analogous to plant and green algae state transitions, has frequently been proposed (Fig. 4).…”

Cyanobacterial Phycobilisome Allostery as Revealed by Quantitative Mass Spectrometry

“…PBSs are only functionally intact in the presence of high phosphate buffer or its variant buffers, , making interrogations on protein conformational changes of PBS in solution very difficult. In my previous report, it was successfully revealed that PB-loop, an IDR in ApcE, is in structural proximity with ApcG, forming a protrusion toward the thylakoid membrane where two photosynthetic RCs are located .…”

“…All PPCs comprise a set of chromophores (or pigments) held in a well-defined protein scaffold. Phycobilisomes (PBSs), giant PPCs with a molecular mass range of 5–15 MDa, − supply excitations to both photosystem I (PSI) and photosystem II (PSII). − PBSs are highly organized assemblies of pigmented phycobiliproteins and pigmentless linker polypeptides. , …”