Many photosynthetic microorganisms have demonstrated the ability to acclimate to light restricted in spectral quality (i.e. red, green, or blue light). Some types of red algae and cyanobacteria are capable of accomplishing this acclimation through rearrangements of their auxiliary light-harvesting antennas made up of phycobiliproteins (PBPs). Because cryptophyte algae lack a macromolecular structure to their PBPs, which are instead dispersed in the thylakoid lumen, it was assumed that they were incapable of this type of acclimation. However, recent work has revealed that cryptophytes can respond to light restricted in spectral quality through an acclimation process resulting in shifts in the absorbance peaks of the PBPs. Here, we reproduce this response in two species of cryptophyte algae, P. sulcata and H. pacifica, and isolate the change associated with this photoacclimation to the level of the individual PBPs. After growth in restricted light conditions, these algae demonstrated shifts in the region of their absorbance spectra associated with their PBPs which were preserved in the spectra of the isolated PBPs. Structural investigations of the acclimated PBPs demonstrated no change in primary or tertiary structure, and analysis of the separated α and β subunit components of the acclimated PBPs revealed the change to be located on the β subunit. The fact that a stable absorption shift response occurred in the absence of a structural change in the protein suggests that cryptophytes are capable of acclimating to changes in the spectral quality of available light through differential chromophorylation of the β subunit.

Controllable phycobilin modification: an alternative photoacclimation response in cryptophyte algae

ACS Fall 2021

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