Lipids driving protein structure? Evolutionary adaptations in Kir channels.

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Phosphatidyl inositol bisphosphate (PIP(2)) is a key regulator of many eukaryotic membrane proteins, including ion channels, transporters, and receptors.
• The eukaryotic inward rectifier potassium (Kir) channel family critically requires membrane PIP(2) for its activity.
• A bacterial homolog, KirBac1.1, exhibits unique inhibition by PIP(2), contrasting with eukaryotic channel activation.

Purpose of the Study:

• To investigate the evolutionary adaptations in eukaryotic potassium channels that enable PIP(2) activation.
• To understand the structural basis for the switch from PIP(2) inhibition to activation during evolution.
• To explore the role of membrane charge in the evolution of eukaryotic channel function.

Main Methods:

• Analysis of new crystal structures of eukaryotic Kir channels.
• Comparative analysis of bacterial (KirBac1.1) and eukaryotic Kir channel structures.
• Bioinformatic analysis of linker regions between transmembrane and cytoplasmic domains.

Main Results:

• New crystal structures reveal additional linker regions in eukaryotic channels between transmembrane and cytoplasmic domains.
• These linkers are hypothesized to be a key evolutionary adaptation converting PIP(2) inhibition to activation.
• This adaptation is proposed to be essential for channel function in the negatively charged eukaryotic membranes.

Conclusions:

• Evolutionary changes in protein structure, specifically the insertion of linkers, enabled eukaryotic channels to utilize PIP(2) as an activator.
• This adaptation was crucial for the functional integration of ion channels within the distinct lipid environment of eukaryotic cell membranes.
• The findings highlight a novel evolutionary pathway driven by changes in membrane composition and protein structure.