[W1] Workshop 1
Unexpected operation mechanism of supramolecular machinery working in cell membrane

[W1-3] Bacterial calcium channels indicate the universal mechanism of calcium-selective ion permeation

Katsumasa Irie (Dept. Biophys. Chem., Sch. Pharm., Wakayama Med. Univ.)

Prokaryotic ion channels play an important role in the structural biology of ion channels. At the end of the 20^th century, the first structure of a prokaryotic ion channel was revealed. Subsequently, the reporting of structures of various prokaryotic ion channels have provided fundamental insights into the structure of ion channels of higher organisms. Similar to other proteins, voltage-dependent Ca²⁺ channels (Cavs) were predicted to have a prokaryotic counterpart; however, it has taken more than 20 years for one to be identified. Cavs are indispensable for coupling action potentials with Ca²⁺ signaling.
CavMr is a firstly identified native prokaryotic Cav as homotetramer. Its selectivity filter contains a smaller number of negatively charged residues than mutant Cavs generated from other prokaryotic channels. CavMr belonged to a different cluster of phylogenetic trees than canonical prokaryotic cation channels. The glycine residue of the CavMr selectivity filter is a determinant for Ca²⁺ selectivity. This glycine residue is conserved among eukaryotic Cavs, suggesting that there is a universal mechanism for Ca²⁺ selectivity. The investigation of these channels can help to understand the mechanism for ion selection that is conserved from prokaryotes to eukaryotes.