Ion channels are integral membrane proteins. A hollow centre through the channel protein forms a water-filled pore through which ions permeate. Ion channels are referred to by the type of permeating ion. K+ channels specifically allow potassium ions to cross the cell membrane through a water-filled channel protein.

Biophysical and biochemical analyses suggested that voltage-gated and inward rectifier K+ channel protein complexes exist as tetrameric structures, consisting of four separate pore forming or principal subunits (also called alpha-subunits) arranged symmetrically around a central pore. This tetrameric channel structure was recently confirmed experimentally with the crystallization and high-resolution structural analysis of a prokaryotic K+ channel from Streptomyces lividans (Doyle et al., 1998) - the first natural membrane channel for which high resolution structural information became available. In addition to these principal subunits, many K+ channel protein complexes also contain auxiliary proteins (sometimes also referred to as beta-subunits) that can significantly modify the properties of the channel complex.

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Principal subunits of potassium channel proteins
Auxiliary subunits that regulate their function and expression