Phycobilisome energy transfer

In contrast to the photosynthetic eukaryotes, photoprotection in cyanobacteria is not induced by the presence of a transthylakoid ApH or the excitation pressure on PSII. Instead, intense blue-green light (400-550 nm) induces a quenching of PSII fluorescence that is reversible in minutes even in the presence of translation inhibitors (El Bissati et al. 2000). Fluorescence spectra measurements and the study of the NPQ mechanism in phycobilisome- and PSII-mutants of the cyanobacterium Synechocystis PCC6803 indicate that this mechanism involves a specific decrease of the fluorescence emission of the phycobilisomes and a decrease of the energy transfer from the phycobilisomes to the RCs (Scott et al. 2006, Wilson et al. 2006). The site of the quenching appears to be the core of the phycobilisome (Scott et al. 2006, Wilson et al. 2006, Rakhimberdieva et al. 2007b). 

Mullineaux, C. W. (1992). Excitation energy transfer from phycobilisomes to photosystem-I in a cyanobacterium. Biochim Biophys Acta 1100(3) 285-292. 

Ashby, M. K., and Mullineaux, C. W. 1999. Cyanobacterial ycf27 gene products regulate energy transfer from phycobilisomes to photosystems I and II. FEMSMicrobiol. Lett. 181, 253-260. 

Major steps in the energy transfer pathway in Synechocystis 6701 phycobilisomes... 

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... 

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. 

D. Energy Transfer between Chromophores in Anabaena variabilis Phycobilisomes.266... 

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. 9. Schematic representation of the phycobiiisome from Anabaena variabilis showing the location of the billproteins and linker polypeptides. See text for details. Adapted from Glazer (1984) Phycobilisomes A macmmolecular complex optimized for light energy transfer. Biochim Biophys Acta 768 42.

II.D. Energy Transfer among Chromophores in Anabaena Variabilis Phycobilisomes... 

Fig. 12. (A) Time-resolved fluorescence spectra of A. nidulans phycobilisomes measured at 77 K. Excitation by 6-ps, 580-nm argon laser pulse. Three small ticks in the topmost spectrum (at 932 ps) indicate locations of maximum fluorescence at 0 ps. (B) Rise and decay of various fluorescent components derived from deconvolution of the fluorescence spectra. Assignment of individual fluorescent components are shown in the right margin. (C) Energy flow among individual chromophores in the phycobilisomes. The asterisk in (B) and (C) indicates a linker polypeptide is attached to the trimer. See text for discussion. Figure source Mimuro (1989) Studies on excitation energy How in the photosynthetic pigment system structure and energy transfer mechanisms. Bot Mag Tokyo 103 244.

AN Glazer(1984) Phycobilisomes A molecular complex optimized for light energy transfer. Blochlm Blophys Acta 768 29-51... 

DJ Lundell, RC Williams and AN Glazer (1981) Molecular architecture of a light-harvesting antenna. In vitro assembly of the rod substructures of Synechococcus 6301 phycobilisomes. J Biol Chem 256 3580-3592 S Brody and E Rabinowitch (1957) Excitation lifetime of photosynthetic pigments. Science 125 555 G Tomita and E Rabinowitch (1962) Excitation energy transfer between pigments in photosynthetic cells. Biophys J 2 483-499... 

G Porter, CJ Treadwell, GFW Searle and J Barber (1978) Picosecond time-resolved energy transfer in Porphyridium cruentum. Part I. In the intact alga. Biochim Biophys Acta 501 232-245 M Mimuro, I Yamazaki, N Tamai and T Katoh (1989) Excitation energy transfer in phycobilisomes at-196 C isolated from the cyanobacterium Anabaena variabilis (M-3) evidence for the plural transfer pathways to the terminal emitters. Biochim Biophys Acta 973, 153-162... 

Swanson, R, V, Glazer, A, N, (1990), Phycobiliprotein methylation. Effect of the y-N-methy-lasparagine residue on energy transfer in phycocyanin and the phycobilisome. J. Mol. Biol. 214, 787-796. 

PSII/PSI ratio 1500. The main pigments were phycocyanin (PC), allo-phycocyanin (AP) and chlorophyll (Chl). When excited at 445 nm the PSII preparations showed a minor fluorescence emission maximum at 660 nm characteristic for allophycocyanin and two major maxima at 685 and 693 nm The fluorescence at 685 nm was attributed to an interplay of allophycocyanin B, the large membrane-phycobilisome linker (Lem) and a Chl-antenna, whilst the 693 nm fluorescence belonged to a Chl-antenna alone. Most of the light energy captured by phycobilisomes was transferred to the final phycobilisome emitters and the PSII antennae as shown from the emission peak at 685 nm and the shoulder at 692 nm. 

EXCITATION ENERGY TRANSFER AMONG PHYCOBILISOMES FROM THE PHYCOERYTHRIN CONTAINING STRAIN ANABAENA VARIABILIS ARM310... 

---