Influence of chromophores on quarternary structure of phycobiliproteins from the cyanobacterium, Mastigocladus laminosus

Chromophores of C-phycocyanin and phycoerythrο-cyanin have been chemically modified by reduction to rubins , bleaching , photoisomerization , or perturbation with bulky substituents. Pigments containing modified chromophores, or hybrids containing modified and unmodified chromophores in individual protomers have been prepared. All modifications inhibit the association of the (aß)-protomers of these pigments to higher aggregates. The results demonstrate a pronounced effect of the state of the chromophores on biliprotein quaternary structure. It may be important in phycobi1isome assembly , and also in the dual function of biliproteins as (i) antenna pigments for photosynthesis and (ii) reaction centers for photomor-phogenesis

Flow of excitation energy in the cryptophyte light-harvesting antenna phycocyanin 645.

We report a detailed description of the energy migration dynamics in the phycocyanin 645 (PC645) antenna complex from the photosynthetic alga Chroomonas CCMP270. Many of the cryptophyceae are known to populate greater depths than most other algal families, having developed a 99.5% efficient light-harvesting system. In this study, we used femtosecond time-resolved spectroscopy and global analysis to characterize the excited-state dynamics of PC645. Several different pump colors were selected to excite different fractions of the four phycobiliprotein pairs present in the complex. Measurements were also performed at cryogenic temperature to enhance spectral resolution and selectively promote downhill energy transfers. Upon excitation of the highest-energy bilins (dihydrobiliverdins), energy is transferred from the core of the complex to the periphery within 0.82 ps. Four bilins (mesobiliverdin (MBV) A/B and phycocyanobilins (PCB) 158C/D), which are responsible for the central band of the absorption spectrum, show concerted spectral dynamics. These chromophores show a biphasic decay with lifetimes of 0.6 ps (MBV) and 5-7 ps (PCB 158) to the lowest bilin pair (PCB 82C/D) absorbing around 650-657 nm. Within this lifetime of several picoseconds, the excitations reach the PCB 82 bilins on the two poles at the smaller sides of PC645. A slow 44-46 ps energy transfer step to the lowest-energy PCB 82 bilin concludes the dynamics. © 2011 Biophysical Society