Irie Katsumasa
Department of Biophysical Chemistry, School of Pharmaceutical Sciences, Wakayama Medical University, Wakayama 640-8156, Japan.
Cellular and Structural Physiology Institute (CeSPI), Nagoya University, Nagoya, Aichi 464-8601, Japan.
Biophys Physicobiol. 2021 Nov 19;18:274-283. doi: 10.2142/biophysico.bppb-v18.033. eCollection 2021.
Prokaryotic channels play an important role in the structural biology of ion channels. At the end of the 20 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. Voltage-dependent Ca channels (Cavs) are indispensable for coupling action potentials with Ca signaling. Similar to other proteins, Cavs were predicted to have a prokaryotic counterpart; however, it has taken more than 20 years for one to be identified. The homotetrameric channel obtained from generates the calcium ion specific current, so it is named as CavMr. 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 calcium selectivity. This glycine residue is conserved among eukaryotic Cavs, suggesting that there is a universal mechanism for calcium selectivity. A family of homotetrameric channels has also been identified from eukaryotic unicellular algae, and the investigation of these channels can help to understand the mechanism for ion selection that is conserved from prokaryotes to eukaryotes.
原核生物通道在离子通道的结构生物学中发挥着重要作用。20世纪末，首个原核生物离子通道的结构被揭示。随后，各种原核生物离子通道结构的报道为高等生物离子通道的结构提供了基本见解。电压依赖性钙通道（Cavs）对于将动作电位与钙信号传导偶联至关重要。与其他蛋白质类似，预计Cavs有原核生物对应物；然而，花了20多年才鉴定出一个。从[具体来源未提及]获得的同四聚体通道产生钙离子特异性电流，因此被命名为CavMr。其选择性过滤器中带负电荷的残基数量比从其他原核生物通道产生的突变型Cavs少。与典型的原核生物阳离子通道相比，CavMr属于不同的系统发育树簇。CavMr选择性过滤器的甘氨酸残基是钙选择性的决定因素。该甘氨酸残基在真核生物Cavs中保守，表明存在钙选择性的普遍机制。还从真核单细胞藻类中鉴定出一个同四聚体通道家族，对这些通道的研究有助于理解从原核生物到真核生物保守的离子选择机制。
