Phycobilisomes structure

Table 1. Examples drawn from four classes of phycobiliproteins, allophycocyanin (APC), phycocyanin (PC), phycoerythrocyanin (PEC), and phycoerythrin (PE), arranged in the order of decreasing wavelengths of their major absorption bands. and x " are the peak wavelengths of the principal (and minor) absorption and fluorescence bands, respectively. See List of Abbreviations for the full names of the different phycobiliproteins. Table adapted from Glazer (1982) Phycobilisomes Structure and dynamics. Annu Rev Microbiology 36 178 and Glazer (1989) Light guides. Directionai energy transfer in a photosynthetic antenna. J Biol Chem. 264 2.

Fig. 8. Representations for the phycobilisome rod components and linker polypeptides (A) and mechanism of assembly (B). Figure adapted from Mdrschel and Rhiel (1987) Phycobilisomes and thylakoids The light-harvesting system of cyanobacteria and red algae. In JR Harris and RW Horne (eds) Membranous Structure, p 238. Acad Press drawn after results of Glazer (1982) Phycobilisomes structure and dynamics. Annu Rev Microbiol 36 183...

Fig. 10. Aggregation behavior of Anabaena variabilis phycocyanin compiexes with the 32.5- and 27-kDa linker poiypeptide after tryptic degradation. Original data from Yu and Glazer (1982) Cyanobactehal phycobilisomes. Roles of the linker polypeptides in the assembly of phycocyanin. J Biol Chem 257 3430 and Glazer (1982) Phycobilisomes structure and dynamics. Annu Rev Microbiol 36 189. Figure drawn in a form similar to that of Fig. 8, using the graphic representation of MSrschel and Rhiel.

The concentration of PSII centres was determined by flash light induced oxygen evolution (7) and correlated with the amount of AP. A Chi to PSII ratio of 120 Chi a/PSII was determined. The molar ratio of PSII to AP was 1 5 Hemi-ellipsoidal phycobilisomes may contain 20-24 moles of AP. Thus the molar ratio of PSII to AP is 4 20 and consequently a tetrameric PSII particle package binds one hemi-ellipsoidal phycobilisome. It is supposed that the aggregation of PSII to dimers and tetra-mers is induced by the phycobilisome structures of the cores. Depending on the type of phycobilisome, different aggregation patterns are realized. 

Fig. 1. Model of phycobilisome structure CP = core protein, probably allophycocyanin PC = phycocyanin PE = phycoerythrin...

Glazer AN. Adaptive variations in phycobilisome structure. Adv Mol Cell Biol (Barber J, ed.). 1994 10 119-149. JAI Press, London. 

Miskiewicz E, Ivanov AG, and Huner NPA. Stoichiometry of the photosynthetic apparatus and phycobilisome structure of the cyanobacterium Plectonema boryanum UTEX 485 are regulated by both light and temperature. Plant Physiol. 2002 130 1414-1425. 

Yamanaka G and Glazer AN (1981) Dynamic aspects of phycobilisome structure. Phycobilisome turnover during nitrogen starvation in Synechococcus sp. Arch Microbiol 124 39-47. 

When complete cells are treated with levulinic acid, a set of 11 peptides are lost from the membrane fraction. The same is true for recovering cells. Since the phycobiliproteins figure so prominently in this set, phycobilisome assembly must be extremely sensitive to levulinic acid. Yamanaka et al. (1978) investigated the phycobilisome structure of a related A. nidulans strain and observed 5 non-pigmented polypeptides. Interestingly, a several peptides lost by inhibition (71, 35, and 27 kDa) are similar in molecular size to peptides observed in the phycobilisome. 

Despite their absence in phycobilisomes, carotenoids, especially the so-called secondary carotenoids such as echinenone, were presumed to play a role in cyanobacterial photoprotection. Indeed, classic biochemical approaches have led to several reports of cyanobacterial carotenoid-proteins and evidence for their photoprotective function (Kerfeld et al. 2003, Kerfeld 2004b). One of these, the water soluble orange carotenoid protein (OCP), has been structurally characterized and has recently emerged as a key player in cyanobacterial photoprotection. 

The known structure of the OCP is a snapshot of the presumably dark-state-adapted form of the protein. From the model, it is difficult to imagine how the concealed carotenoid could interact with one of the components of the phycobilisome in order to quench the absorbed energy. However, the surface of the OCP has numerous surface cavities and clefts, as shown in Figure 1.3b, including two... 

Adir, N. (2005). Elucidation of the molecular structures of components of the phycobilisome Reconstructing a giant. Photosynth Res 85(1) 15-32. 

FIGURE 19-43 A phycobilisome. In these highly structured assemblies found in cyanobacteria and red algae, phycobilin pigments bound to specific proteins form complexes called phycoerythrin (PE), phycocyanin (PC), and allophycocyanin (AP). The energy of photons absorbed by PE or PC is conveyed through AP (a phycocyanobilin-binding protein) to chlorophyll a of the reaction center by exciton transfer, a process discussed in the text. 

Bryant, D. 1991. Cyanobacterial phycobilisomes progress toward complete structural and functional analysis via molecular genetics. In Bogorad L. and Vails IK (eds) Cell Structure Somatic Cell Genetics of Plants, Vol. 7B (The Photosynthetic Apparatus Molecular Biology and Operation), pp 257-300. Academic Press, New York. 

Carotenoids are found in all native photosynfhetic organisms. They serve a dual function, as both accessory antenna pigment and also are essential in photoprotection of photosynfhetic systems from the effects of excess light, especially in the presence of oxygen. Bilins are open-chain tetrapyrroles that are present in antenna complexes called phycobilisomes. These complexes are found in cyanobacteria and red algae. Structures of representative carotenoid pigments are shown in Figure 3. 

Figure 8 (a) Structure of the phycocyanin antenna complex from the cyanobacterimn Synechocystis 6701 and proposed structure of the complex from Thermosynechocystis vulgaris, (Ref. 32. Reproduced by permission of American Society for Biochemistry Molecular Biology), (b) Energy transfer route in the phycobilisomes. (c) Crystal structure of the allophycocyanin a-subunit. (d) Crystal structure of the allophycocyanin /3-subunit, (e) Hexameric arrangement of three a/8 units to make the disc-like aP)-i hexamer... 

Fig. 11. Phycobilisome of Masligocladus laminosus (Fischerella PCC 7603) represented in a schematic view. The structure is adapted from the PBS of Synechocystis 6701 [77] using structural and spectral data from M. laminosus biliproteins and linker polypeptides [22,31,82,97,105,135-137]. For the designation of the rod and core substructures, the nomenclature of Glazer [86] is applied.

The subject of energy transfer in phycobilisomes and their sub-structures already has a large literature (see Ref. 65 for a review), mostly beyond the scope of this chapter. However, two of these sub-structures - trimeric C-phycocyanin from the thermophilic cyanobacterium Mastigocladus laminosus and hexameric C-phycocyanin from the cyanobacterium Agmenellum quadruplicatum-have very recently become respectively the third and fourth photosynthetic pigment-protein complexes for which structural models based on single-crystal X-ray diffraction near atomic resolution are now available (Refs. 66,67 and Chapter 11). Since these are presently the only such complexes, in addition to the two already discussed (Sections 5 and 6), it seems appropriate to conclude this review of exciton effects with some brief remarks on these C-phycocyanin structures. 

Figure 19.31. Structure of a Phycobilisome Subuuit. This protein, a phycoerythrin, contains a phycoerythrobilin linked to a cysteine residue. The inset shows the absorption spectrum of a phycoerythrin. 

Figure 19.32. Structure of a Phycobilisome. (A) Electron micrograph of phycobilisomes from a cyanobacterium (Synechocystis). (B) Schematic representation of a phycobilisome from the cyanobacterium 6701. Rods...

As the supramolecular structure of phycobilisomes is formed, the absorption in the visible region is further enhanced. Apparently, the absorption is influenced by interaction ofthe chromophore with the protein environment, resulting also in a significant red shift ofthe absorption bands and a higher fluores-... 

---