Novel pH-Sensitive Microbial Rhodopsin from Sphingomonas paucimobilis

Area of Science:

• Microbiology
• Biochemistry
• Structural Biology

Background:

• Sphingomonas paucimobilis is an aerobic bacterium linked to opportunistic infections.
• Rhodopsins are microbial membrane proteins with diverse functions.
• The SpaR rhodopsin from S. paucimobilis has not been previously characterized.

Purpose of the Study:

• To characterize the novel rhodopsin SpaR from Sphingomonas paucimobilis.
• To investigate the functional properties and pH-dependent behavior of SpaR.
• To explore the potential applications of SpaR in basic research and optogenetics.

Main Methods:

• Sequence analysis of the SpaR protein.
• Functional assays to determine proton pumping activity at different pH levels.
• Photocycle analysis in detergent micelles to study pH-dependent kinetics.

Main Results:

• SpaR possesses an unusual DTS motif, not previously reported in Proteobacteria rhodopsins.
• SpaR functions as an outward proton pump, primarily active at low pH.
• Proton pumping is significantly reduced at neutral and alkaline pH.
• The rhodopsin photocycle slows with increasing pH due to extended Schiff base reprotonation.

Conclusions:

• SpaR is a novel microbial ion transporter with unique characteristics.
• Its pH-dependent proton pumping activity makes it an interesting subject for membrane protein research.
• SpaR holds promise as a potential optogenetic tool due to its functional properties.