Cyanobacterial Phycobilisomes

Abstract

Cyanobacterial phycobilisomes harvest light and cause energy migration usually toward photosystem II reaction centers. Energy transfer from phycobilisomes directly to photosystem I may occur under certain light conditions. The phycobilisomes are highly organized complexes of various biliproteins and linker polypeptides. Phycobilisomes are composed of rods and a core. The biliproteins have their bilins (chromophores) arranged to produce rapid and directional energy migration through the phycobilisomes and to chlorophyll a in the thylakoid membrane. The modulation of the energy levels of the four chemically different bilins by a variety of influences produces more efficient light harvesting and energy migration. Acclimation of cyanobacterial phycobilisomes to growth light by complementary chromatic adaptation is a complex process that changes the ratio of phycocyanin to phycoerythrin in rods of certain phycobilisomes to improve light harvesting in changing habitats. The linkers govern the assembly of the biliproteins into phycobilisomes, and, even if colorless, in certain cases they have been shown to improve the energy migration process. The Lcm polypeptide has several functions, including the linker function of determining the organization of the phycobilisome cores. Details of how linkers perform their tasks are still topics of interest. The transfer of excitation energy from bilin to bilin is considered, particularly for monomers and trimers of C-phycocyanin, phycoerythrocyanin, and allophycocyanin. Phycobilisomes are one of the ways cyanobacteria thrive in varying and sometimes extreme habitats. Various biliprotein properties perhaps not related to photosynthesis are considered: the photoreversibility of phycoviolobilin, biophysical studies, and biliproteins in evolution. Copyright 1998 Academic Press.

A low molecular weight protein tyrosine phosphatase from Synechocystis sp. strain PCC 6803: enzymatic characterization and identification of its potential substrates

“…PCC 6803 and functions as a light harvesting antenna for the transfer of the excitation energy to photosynthetic reaction centres (50,52). It is known that in green plants, phosphorylation of proteins in the light harvesting complex II (LHCII) regulate the distribution of absorbed excitation energy between photosystem I (PSI) and photosystem II (PSII) such that light-limited photosystem receives more energy, while the light-saturated photosystem receives less (53).…”

Acclimation of unicellular cyanobacteria to macronutrient deficiency: emergence of a complex network of cellular responses

“…Nitrogen and sulfur starvation, on the other hand, elicit substantial pigment loss in Synechococcus, with nitrogen depletion inducing rapid and complete phycobilisome degradation (Collier & Grossman, 1992). The phycobilisome is an ultrastructure consisting of pigmented proteins (phycobiliproteins) as well as nonpigmented (linker) polypeptides (Glazer, 1985;Grossman et al, 1993;MacColl, 1998). The rapid and complete degradation of this abundant complex, which may constitute up to 50 % of soluble cellular protein, indicates the existence of highly effective degradation machinery.…”

Structural organization of an intact phycobilisome and its association with photosystem II

“…Phycobilisomes (PBSs) are attached to the cytoplasmic surface of thylakoid membranes and are responsible for the majority of light capture for photosynthesis in cyanobacteria and red algae [1][2][3]. A hemidiscoidal PBS, which is the most common PBS type, has two parts: the core and the peripheral rods.…”

“…PBPs are brilliantly colored, water-soluble proteins bearing different numbers of chromophores, which are open-chain tetrapyrroles covalently bound to cysteine residues via thioether bonds [22]. Based on the bilin energy level, PBPs are mainly categorized into three types: phycoerythrins (PEs) or phycoerythrocyanins at the core-distal ends of rods (which absorb high-energy light), phycocyanins (PCs) at the core-adjacent portions of rods (which absorb intermediate-energy light), and allophycocyanins (APCs), the major components of the core (which absorb low-energy light) [1]. Although PBPs have different absorption spectra due to different bilin energy levels, they have similar crystal structures [7,8] and assemble into PBSs through a common hierarchical organization.…”