Functional Green-Tuned Proteorhodopsin from Modern Stromatolites

Area of Science:

• Microbiology
• Biophysics
• Extremophile Research

Background:

• Exiguobacterium sp. S17, a poly-extremophile, was isolated from stromatolites in a High-Altitude Andean Lake (HAAL).
• The HAAL environment experiences extreme UV irradiation, posing survival challenges for microbial communities.

Purpose of the Study:

• To investigate a putative proteorhodopsin-encoding gene found in the Exiguobacterium sp. S17 genome.
• To characterize the biophysical and photochemical properties of the expressed proteorhodopsin.

Main Methods:

• Heterologous expression of the Exiguobacterium proteorhodopsin (E17R).
• Spectroscopic analysis (UV-Vis absorption, laser flash-induced absorption changes) to determine spectral properties and reaction kinetics.
• Biomembrane 전류 (BLM) measurements to assess proton transport capability.

Main Results:

• E17R assembled with retinal, showing an absorbance maximum at 524 nm, classifying it as a green-absorbing proteorhodopsin.
• The protein exhibited a pK value between 2 and 3.
• Kinetic analysis revealed multiple red-shifted intermediates with decay times ranging from microseconds to milliseconds.
• Proton transport was confirmed, with evidence of a blue light-absorbing, M-like intermediate.

Conclusions:

• The study characterizes a novel proteorhodopsin from a high-altitude extremophile, contributing to understanding microbial adaptation.
• The identified proteorhodopsin demonstrates functional proton transport and unique photochemical properties under simulated extreme conditions.