Researchers provided data to show that Ca2 binds to the BK c

Researchers provided data to show that Ca²⁺ binds to the BK channel at 2 specific sites.

Discuss how for awhile, the functional data in support of 2 separate calcium binding sites did not match the structural data. Describe both the functional (electrophysiology) and structural data and how scientists tried to make sense of the contradiction.

Solution

The BKca channel is at the core of a voltage-gated K+ channel complete with amphipathic S4 helix and K+ channel pore sequence. The BKca channel has a very large single channel conductance. It has beta subunits that dramatically influence gating and has evolved a very large COOH terminal cytoplasmic domain, presumably for calcium sensing.

The Ca+2 sensing properties of BKca channel segregate with the channel\'s cytoplasmic domain but not its integral membrane domain and there is an acidic region in this cytoplasmic domain where mutations alter Ca+2 sensing.

The research provides that BKca channel has two types of high affinity Ca+2 binding sites each with a different selectivity for divalent cations.