Energy transfer dynamics in B-phycoerythrin from the red alga Porphyridium purpureum

Abstract

The B-phycoerythrin hexamer (αβ) 6 γ of Porphyridium purpureum was isolated and purified. The absorption, circular dichroism, fluorescence and ultrafast time-resolved spectra were obtained. The results showed a double absorption peak at 545 nm and 565 nm and a shoulder peak at 498 nm, and fluorescence emission maxima at 580 nm and 620 nm were observed. The circular dichroism spectra in the near-ultraviolet region were obtained and resolved for the first time, which showed that the two peaks at 260 nm and 305 nm were considered to be correlated to phenylalanine (Phe) and tryptophan (Trp) in a conservative hydrophobic microenvironment, respectively. The circular dichroism spectra in the visible region showed that PEB139α/PEB158β and PEB82α/PEB82β existed as two exciton-coupled bilin pairs. Energy transfer within the exciton-coupled pairs was by exciton splitting, while between the exciton-coupled pairs was by Förster resonance. From the studies of the energy transfer dynamics by ultrafast time-resolved fluorescence spectroscopy, it was confirmed that the energy transfer of the B-PE hexamer had three time components of 8 ps, 60 ps, and 1200 ps. In addition, the internal energy transfer pathways of B-phycoerythrin hexamer were identified by deconvoluting the fluorescence decay curve at different detection wavelengths.

The structural basis for light acclimation in phycobilisome light harvesting systems systems in Porphyridium purpureum

“…1 ), in which the ML cells are shown to have less phycoerythrin pigments per cell than LL. They also correspond to previous knowledge on light adaptation, where increasing the light intensity can result in loss of subunits and shorter rods in red algae 39 and marine Synechococcus 40 , 41 . The difference in the effective absorption cross-section between ML and LL PBS structures is in line with the difference in the excitation pressure between the two growth conditions.…”

Difference in light use strategy in red alga between Griffithsia pacifica and Porphyridium purpureum

“…According to the above steady-state absorption spectra, it is obviously that R-PE is more dominated in G. pacifica PBSs than B-PE, and so does for B-PE in P. purpureum PBSs. Furthermore, the α subunit of B-PE contains two PEBs, the β subunit of B-PE contains three PEBs, whereas γ subunit CONTAINS two PEBs and two PUBs 21 . The type and position of chromophore in R-PE are similar to those in B-PE.…”

“…The maximum of the fluorescence evolved the red-shift gradually. According to the research results of PBPs 21 , when PUB of PE is excited under pump wavelength of 498 nm, the excited energy could be transferred through intra-protein pathway from PUB to PEB and display a terminal emission at around 570 nm, and this intra-protein energy transfer can be very fast. The peak is then slowly red-shifted from 570 to 580 nm, and the fluorescence band broadens until it is separated into two bands.…”

Exploring and strengthening the potential of R-phycocyanin from Nori flakes as a food colourant

“…The specific feature of R-PC is the presence of additional bands in absorption, fluorescence and CD spectra, arising from the PEB chromophore, not presented in the cyanobacterial phycocyanins (Yan et al, 2010). The different peak positions between near-UV-VIS CD and absorption spectra of R-PC indicate strong exciton-type interactions between tetrapyrrole chromophores, confirming the oligomeric structure of the protein (Glazer et al, 1975;Li et al, 2020).…”