Structural Foundations of Potassium Selectivity in Channelrhodopsins

Area of Science:

• Molecular Biology
• Neuroscience
• Biophysics

Background:

• Potassium-selective channelrhodopsins (KCRs) are light-gated K⁺ channels from the protist Hyphochytrium catenoides.
• KCRs enable precise optogenetic inhibition of neuronal activity without traditional K⁺ selectivity filters.
• These channels offer potential for treating neurological and cardiovascular disorders.

Purpose of the Study:

• To identify the structural motifs responsible for the unique K⁺ selectivity of KCRs.
• To understand the mechanism of K⁺/Na⁺ discrimination in these channels.
• To lay the groundwork for engineering KCRs for advanced optogenetic applications.

Main Methods:

• Systematic analysis of KCR chimeras and mutants.
• Characterization of homologous proteins from other protists and metagenomic samples.
• Site-directed mutagenesis to probe the function of specific residues.

Main Results:

• Mutations in three critical residues converted a Na⁺-selective paralog into a K⁺-selective channel.
• These residues, along with conserved Trp102 and Asp116, are crucial for K⁺ selectivity across different KCR homologs.
• An alternative K⁺ selectivity mechanism, distinct from classical filters, was confirmed.

Conclusions:

• Specific amino acid residues dictate K⁺ selectivity in KCRs, offering a novel mechanism.
• The identified structural motifs are essential for KCR function and can be leveraged for engineering.
• This research advances the development of KCRs as powerful optogenetic tools.