A native prokaryotic voltage-dependent calcium channel with a novel selectivity filter sequence

Voltage-dependent Ca(2+) channels (Cavs) are indispensable for coupling action potentials with Ca(2+) signaling in living organisms. The structure of Cavs is similar to that of voltage-dependent Na(+) channels (Navs). It is known that prokaryotic Navs can obtain Ca(2+) selectivity by negative charge mutations of the selectivity filter, but native prokaryotic Cavs had not yet been identified. We report the first identification of a native prokaryotic Cav, CavMr, whose selectivity filter contains a smaller number of negatively charged residues than that of artificial prokaryotic Cavs. A relative mutant whose selectivity filter was replaced with that of CavMr exhibits high Ca(2+) selectivity. Mutational analyses revealed that the glycine residue of the CavMr selectivity filter is a determinant for Ca(2+) selectivity. This glycine residue is well conserved among subdomains I and III of eukaryotic Cavs. These findings provide new insight into the Ca(2+) selectivity mechanism that is conserved from prokaryotes to eukaryotes.