Probing algae structure with fluorescence spectroscopy

Cryptophytes are a type of photosynthetic algae common in diverse aquatic environments. They generate energy thanks to a densely packed group of light-harvesting proteins called phycobiliproteins, which exist untethered inside chloroplasts. As a result, phycobiliproteins often change position and orientation and need to maintain their efficiency in multiple different arrangements.

Moya et al. used single-molecule fluorescence spectroscopy to map the conformational dynamics in one phycobiliprotein, phycoerythrin 545. They identified three types of transition between three possible states.

“We could divide individual proteins into different states: unquenched, quenched, and off,” said author Gabriela Schlau-Cohen. “A protein switching between the quenched and unquenched state was consistent with structural reorganization of the protein, whereas switching between other states was ascribed to blinking or the pigments photobleaching.”

Tracking how these proteins transition between states can provide clues to the structure of cryptophytes and how they successfully arrange their light-harvesting proteins without any substantial scaffolding. It could also explain why cryptophytes evolved to have this unique mechanism for photosynthesis.

“Identifying how the protein conformations fluctuate within this soluble environment may reveal advantages to this architecture,” said Schlau-Cohen. “We hope that this will help with further investigations into cryptophytes, and even suggest new directions for investigation, such as when the different conformations become dominant and how they help in a given microenvironment.”

The researchers plan to examine other cryptophyte proteins and study the conformational dynamics under a wider range of conditions. They hope these future studies will enable better technologies for harnessing energy in disordered and chaotic environments.

Source: “Observation of conformational dynamics in single light-harvesting proteins from cryptophyte algae,” by Raymundo Moya, Audrey C. Norris, Leah C. Spangler, Gregory D. Scholes, and Gabriela S. Schlau-Cohen, Journal of Chemical Physics (2022). The article can be accessed at https://doi.org/10.1063/5.0095763 .

This paper is part of the Photosynthetic Light-Harvesting and Energy Conversion Collection, learn more here .