Functional characterization of sodium-pumping rhodopsins with different pumping properties

Area of Science:

• Biophysics
• Optogenetics
• Microbial Biochemistry

Background:

• Sodium pumping rhodopsins (NaRs) are microbial-type I rhodopsins capable of active ion transport.
• Their ability to transport Na+ and H+ varies with ionic conditions, suggesting diverse functional roles.

Purpose of the Study:

• To investigate the electrophysiological and spectroscopic properties of 12 different NaRs.
• To evaluate the potential of NaRs as optogenetic tools for controlling neuronal activity.

Main Methods:

• Surveyed 12 NaRs for photocurrents in mammalian cells.
• Characterized four promising NaRs using electrophysiology and spectroscopy.
• Assessed functional expression and light-induced hyperpolarization in hippocampal neuron cultures.

Main Results:

• Four NaRs exhibited Na+-based photocurrents with membrane potential-sensitive turnover rates.
• The NaR from Salinarimonas rosea showed red-shifted absorption and slower kinetics than KR2.
• NaRs from Flagellimonas sp_DIK and Nonlabens sp_YIK_SED-11 displayed higher Na+ selectivity.
• All four characterized NaRs successfully hyperpolarized neurons and inhibited spiking, albeit with lower efficiency than proton pumps.

Conclusions:

• NaRs represent a novel class of optogenetic tools for neuronal hyperpolarization.
• These NaRs offer a method for optical control of excitable cells without affecting proton gradients.
• Further research into NaR optimization could enhance their efficiency for optogenetic applications.