A novel six-rhodopsin system in a single archaeon

Area of Science:

• Microbiology
• Biochemistry
• Structural Biology

Background:

• Microbial rhodopsins are photoactive proteins crucial for energy harvesting and sensing across domains of life.
• Nearly 5,000 known rhodopsins perform functions like ion transport and phototaxis, with a maximum of four identified in a single archaeon previously.
• The early Earth environment may have hosted microbial rhodopsins due to their essential functions and resource efficiency.

Purpose of the Study:

• To investigate the microbial rhodopsin system in the archaeon Haloarcula marismortui.
• To characterize the spectral diversity, function, and expression of rhodopsins in H. marismortui.
• To identify novel photoreceptor functions and systems within this archaeon.

Main Methods:

• Identification and expression analysis of six microbial rhodopsins in H. marismortui.
• Overexpression of purified rhodopsins in Escherichia coli for detailed analysis.
• Spectroscopic determination of absorption spectra and photocycle kinetics.
• Measurement of ion transport activity and phototaxis responses.

Main Results:

• A novel system of six microbial rhodopsins was identified and confirmed to be expressed in H. marismortui.
• The identified rhodopsins displayed a broader absorbance spectral distribution than previously known systems.
• Two isochromatic light-driven proton transporters and a new sensory rhodopsin-like transducer were discovered.

Conclusions:

• H. marismortui possesses the most diverse microbial rhodopsin system identified to date in a single archaeon.
• The study reveals a unique proton transport system with co-responding rhodopsins and a novel sensory transducer.
• These findings expand our understanding of microbial photoreceptor diversity and function, particularly in archaea.