Subunit-dependent assembly of inward-rectifier K+ channels

Area of Science:

• Molecular biology
• Neuroscience
• Biophysics

Background:

• Inward-rectifier, G-protein-regulated, and ATP-dependent K+ channels represent a novel gene family with two transmembrane segments.
• These channels are distinct from the six-transmembrane segment voltage-gated Shaker-type K+ channels.
• Quaternary structure of voltage-gated K+ channels is well-studied, but inward-rectifier K+ channel subunit assembly remains largely unknown.

Purpose of the Study:

• To investigate the subunit assembly of inward-rectifier K+ channels.
• To determine the quaternary structure and assembly rules of these channels.
• To analyze the functional consequences of hetero-oligomeric channel formation.

Main Methods:

• Utilized differential sensitivity to voltage-dependent pore block by spermine to analyze subunit assembly.
• Investigated the assembly of 'strong' (BIR10) and 'mild' (ROMK1) inward-rectifier K+ channel subunits.
• Examined co-assembly in auditory hair cells.

Main Results:

• Inward-rectifier K+ channel proteins are composed of four subunits, with assembly generally following binomial distribution rules.
• Co-expressed BIR10 and ROMK1 subunits form hetero-tetramers in auditory hair cells.
• The distribution of these hetero-tetramers deviates from binomial, with hetero- and homo-oligomeric channels forming with similar probabilities.

Conclusions:

• Inward-rectifier K+ channel assembly involves tetrameric structures.
• Hetero-oligomeric channel formation in auditory hair cells leads to independent channel populations with distinct functional properties.
• This provides novel insights into the structural basis of K+ channel diversity and function.