Controllable phycobilin modification: an alternative photoacclimation response in cryptophyte algae

Abstract

Cryptophyte algae are well known for their ability to survive under low light conditions through the use of their auxiliary light harvesting antennas, phycobiliproteins. Mainly acting to absorb light where chlorophyll cannot (500-650 nm), phycobiliproteins also play an instrumental role in helping cryptophyte algae respond to changes in light intensity through the process of photoacclimation. Until recently, photoacclimation in cryptophyte algae was only observed as a change in the cellular concentration of phycobiliproteins; however, an additional photoacclimation response was recently discovered that causes shifts in the phycobiliprotein absorbance peaks following growth under red, blue, or green light. Here, we reproduce this newly identified photoacclimation response in two other species of cryptophyte algae, P. sulcata and H. pacifica, and elucidate the origin of the response on the protein level. We compare isolated native and photoacclimated phycobiliproteins for these two species using spectroscopy and mass spectrometry, and we report the x-ray structures of the PC577 light harvesting complex and corresponding photoacclimated complex. We find that neither the protein sequences, nor the protein structures are modified by photoacclimation. We conclude that cryptophyte algae change a chromophore in one site of their phycobiliprotein beta-subunits as part of the photoacclimation response to changes in the spectral quality of light. Ultrafast pump-probe spectroscopy shows that the energy transfer is weakly affected by the photoacclimation.

Infrared Signatures of Phycobilins within the Phycocyanin 645 Complex

“…Furthermore, depending on the environmental conditions, cryptophytes tune their absorption wavelengths by subtle modifications in chemical structures and protein linkage of the constituent phycobilin chromophores. 4,6,7 This work focuses on the phycobiliprotein phycocyanin 645 (PC645), a light-harvesting complex in the cryptophyte algae Chroomonas mesostigmatica (CCMP269). 6 PC645 employs chromophores with diverse chemical structures as well as strong interpigment coupling to expand its spectral cross section for light absorption.…”

Chirped Laser Pulse Control of Vibronic Wavepackets and Energy Transfer in Phycocyanin 645

“…Since algae use incoherent light as a source for photosynthesis, 63 ultrafast laser experiments do not mimic natural excitation conditions. Prior work 64 has established that cryptophyte algae species undergo photoacclimation in response to different spectral filtering conditions of incoherent light. However, under coherent excitation, vibronic coupling for EET suggests that there is an enhancement of spectral overlap by a vibrational resonance with a frequency of 1580 cm −1 .…”