Structure of the light-driven sodium pump KR2 and its implications for optogenetics

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Cellular ion gradients are vital for life, maintained by active transporters.
• Microbial rhodopsins, including light-driven ion pumps, are key players in this process.
• Cation (sodium) pumps, like KR2, are a recent discovery within this family.

Purpose of the Study:

• To analyze the structural implications of the KR2 sodium pump.
• To understand the mechanism of sodium translocation through KR2.
• To explore optogenetic applications of KR2 and its variants.

Main Methods:

• High-resolution atomic structure determination of the KR2 pump.
• Analysis of the ion translocation pathway, selectivity filter, and binding pockets.
• Design and engineering of KR2 variants for potassium pumping.

Main Results:

• Detailed atomic structures revealed the complete sodium ion translocation pathway in KR2.
• Key structural features include the NDQ triad, ion uptake cavity, N-terminal helix, and flexible retinal-binding pocket.
• KR2 was observed to pentamerize, with sodium ions binding at the interface, and potassium-pumping variants were successfully designed.

Conclusions:

• Structural insights elucidate the sodium translocation mechanism in microbial rhodopsins.
• The findings are crucial for advancing optogenetic applications using KR2 and its engineered variants.