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

Takushi Shimomura,Katsumasa Irie,Yoshiki Yonekawa,Michihiro Tateyama,Hitoshi Nagura,Yoshinori Fujiyoshi

doi:10.7554/elife.52828

Takushi Shimomura, Katsumasa Irie + Show 4 more

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https://doi.org/10.7554/elife.52828

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Abstract

Voltage-dependent Ca2+ channels (Cavs) are indispensable for coupling action potentials with Ca2+ 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 Ca2+ 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 Ca2+ selectivity. Mutational analyses revealed that the glycine residue of the CavMr selectivity filter is a determinant for Ca2+ selectivity. This glycine residue is well conserved among subdomains I and III of eukaryotic Cavs. These findings provide new insight into the Ca2+ selectivity mechanism that is conserved from prokaryotes to eukaryotes.

Highlights

Voltage-dependent Ca2+ channels (Cavs), which couple the membrane voltage with Ca2+ signaling, regulate some important physiological functions, such as neurotransmission and muscle contraction (Hille, 2001)
The channel subunits of both mammalian Cavs and mammalian voltage-dependent Na+ channels (Navs) have 24 transmembrane helices (24TM) (Catterall, 2000), and comprise four homologous subdomains with six transmembrane helices that correspond to one subunit of homotetrameric channels, such as voltage-dependent K+ channels and prokaryotic Navs (BacNavs)
CavMr is the first native prokaryotic Cavs reported, and NavPp could be inhibited by high concentrations of extracellular Ca2+

Summary

Introduction

Voltage-dependent Ca2+ channels (Cavs), which couple the membrane voltage with Ca2+ signaling, regulate some important physiological functions, such as neurotransmission and muscle contraction (Hille, 2001). The channel subunits of both mammalian Cavs and mammalian voltage-dependent Na+ channels (Navs) have 24 transmembrane helices (24TM) (Catterall, 2000), and comprise four homologous subdomains with six transmembrane helices that correspond to one subunit of homotetrameric channels, such as voltage-dependent K+ channels and prokaryotic Navs (BacNavs). Comparison of the sequences of Navs and Cavs indicate that Navs derived from Cavs. Their two pairs of subdomains, domains I and III, and domains II and IV, are evolutionarily close to each other (Rahman et al, 2014; Strong et al, 1993). Prokaryotes are expected to have such ancestor-like channels, native prokaryotic Cavs have not yet been identified. The lack of ancestor-like prokaryotic Cavs is a missing link in the evolution of voltagedependent cation channels

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