Phycobilisome and Phycobiliprotein Structures

Abstract

Phycobilisomes serve as the primary light-harvesting antennae for Photo system II in cyanobacteria and red algae. These supramolecular complexes are primarily composed of phycobiliproteins, a brilliantly colored family of water-soluble proteins bearing covalently attached, open-chain tetrapyrroles known as phycobilins. In addition, phycobilisomes also contain smaller amounts 'linker polypeptides,' most of which do not bear chromophores. These components are absolutely required for proper assembly and functional organization of the structure. Phycobilisomes are constructed from two main structural elements: a core substructure and peripheral rods that are arranged in a hemidiscoidal fashion around that core. The core of most hemidiscoidal phycobilisomes is composed of three cylindrical subassemblies. The peripheral rods radiate from the lateral surfaces of the core substructure which are not in contact with the thylakoid membrane. Absorbed light energy is transferred by very rapid, radiation-less downhill energy transfer from phycoerythrin or phycoerythrocyanin (if present) to C-phycocyanin and then to allophycocyanin species that act as the final energy transmitters from the phycobilisome to the Photo system II or (partially) Photosystem I reaction centers.This chapter focuses on important recent developments concerning the structure and function of phycobilisome architecture and their constituent phycobiliproteins. Studies with the phycobilisomes and phycobiliproteins of the cyanobacterium Mastigocladus laminosus as will be emphasized. During the last decade tremendous progress has been made in the molecular biology of cyanobacteria-through gene

A rising tide of blue‐absorbing biliprotein photoreceptors – characterization of seven such bilin‐binding GAF domains in Nostoc sp. PCC7120

“…The variation of the absorption maxima, including that of the light-activated state of All3691-GAF2 at 490 nm, is well within the range encountered in biliproteins. For example, depending on the apoprotein, PCB shows variations in absorption maxima of approximately 100 nm [44]. However, some of the chromoproteins (All1688 and Alr3356) show unusual photochemistries that require further study.…”

“…All show absorption at approximately 420 nm that is reversible bleached to various degrees by irradiation with blue light (420 nm); the concomitant increases occur at approximately 600 nm (Alr3356), 530-560 nm (All1280, Alr1966 and Alr2279) and even below 500 nm (All3691). The bound parent chromophore(s) were identified after removing non-covalent interactions with the protein by denaturation with acidic urea (8 M, pH 2.0) [44], and then converting any 15E isomers to the respective 15Z isomers by irradiation with 500-570 nm light. All spectra are consistent with the presence of only PCB and/or PVB under these denaturing conditions: the reduction of the band at approximately 420 nm upon denaturation shows that the bond to the second cysteine is lost during the treatment (Fig.…”

Solution‐State 15N NMR Spectroscopic Study of α‐C‐Phycocyanin: Implications for the Structure of the Chromophore‐Binding Pocket of the Cyanobacterial Phytochrome Cph1

“…The different light-absorption characteristics and the specific arrangement of the phycobiliproteins within the phycobilisome enable efficient directional-energy transfer to chlorophyll A, mainly in photosystem II. [4,5] By contrast, phytochromes are not "energy collectors" but sensory biliprotein photoreceptors that act as light-dependent regulators in numerous metabolic pathways in all flowering plants, as well as in cyanobacteria, nonphotosynthetic bacteria, and even fungi. [6] They are able to sense red and far-red light through two spectrally different, photoconvertible isoforms: the P r form, which absorbs red light, and the P fr form, which absorbs far-red light.…”

Purification, crystallization, NMR spectroscopy and biochemical analyses of α‐phycoerythrocyanin peptides

“…With respect to this function they are assembled to supramolecular protein pigment complexes, i.e. phycobilisomes, building up a highly ordered network of very rigid chromophores which enable an energy transfer efficiency of almost 100% [1,2].…”