Department of Biology, University of Toronto Mississauga, Mississauga, Ontario, Canada.
Laboratory of Synaptic Transmission, Krembil Research Institute, Toronto, Ontario, Canada.
J Biol Chem. 2020 Dec 25;295(52):18553-18578. doi: 10.1074/jbc.RA120.015725. Epub 2020 Oct 23.
The dominant role of Ca2 voltage-gated calcium channels for driving neurotransmitter release is broadly conserved. Given the overlapping functional properties of Ca2 and Ca1 channels, and less so Ca3 channels, it is unclear why there have not been major shifts toward dependence on other Ca channels for synaptic transmission. Here, we provide a structural and functional profile of the Ca2 channel cloned from the early-diverging animal , which lacks a nervous system but possesses single gene homologues for Ca1-Ca3 channels. Remarkably, the highly divergent channel possesses similar features as human Ca2.1 and other Ca2 channels, including high voltage-activated currents that are larger in external Ba than in Ca; voltage-dependent kinetics of activation, inactivation, and deactivation; and bimodal recovery from inactivation. Altogether, the functional profile of Ca2 suggests that the core features of presynaptic Ca2 channels were established early during animal evolution, after Ca1 and Ca2 channels emerged via proposed gene duplication from an ancestral Ca1/2 type channel. The channel was relatively insensitive to mammalian Ca2 channel blockers ω-agatoxin-IVA and ω-conotoxin-GVIA and to metal cation blockers Cd and Ni Also absent was the capacity for voltage-dependent G-protein inhibition by co-expressed Gβγ subunits, which nevertheless inhibited the human Ca2.1 channel, suggesting that this modulatory capacity evolved via changes in channel sequence/structure, and not G proteins. Last, the channel was immunolocalized in cells that express an endomorphin-like peptide implicated in cell signaling and locomotive behavior and other likely secretory cells, suggesting contributions to regulated exocytosis.
钙电压门控钙通道在驱动神经递质释放中起主导作用，这一作用在广泛的物种中是保守的。鉴于 Ca2 和 Ca1 通道的功能特性重叠，而 Ca3 通道的重叠性较小，尚不清楚为什么突触传递没有向依赖其他 Ca 通道发生重大转变。在这里，我们提供了一种从早期分化的动物中克隆的 Ca2 通道的结构和功能特征，该动物没有神经系统，但拥有 Ca1-Ca3 通道的单个基因同源物。值得注意的是，高度分化的通道具有与人类 Ca2.1 和其他 Ca2 通道相似的特征，包括在外源性 Ba 中比在 Ca 中更大的高电压激活电流；激活、失活和去活的电压依赖性动力学；以及从失活中恢复的双峰模式。总的来说，Ca2 的功能特征表明，在 Ca1 和 Ca2 通道通过从祖先 Ca1/2 型通道的基因复制出现后，突触前 Ca2 通道的核心特征在动物进化早期就已经确立。该通道对哺乳动物 Ca2 通道阻断剂 ω-芋螺毒素-IVA 和 ω-芋螺毒素-GVIA 以及金属阳离子阻断剂 Cd 和 Ni 相对不敏感；也不存在与共表达的 Gβγ亚基的电压依赖性 G 蛋白抑制能力，尽管如此，它抑制了人类 Ca2.1 通道，这表明这种调节能力是通过通道序列/结构的变化而不是 G 蛋白进化而来的。最后，该通道在表达内吗啡肽样肽的细胞中被免疫定位，该肽与细胞信号转导和运动行为有关，也可能与其他分泌细胞有关，这表明它对调节性胞吐作用有贡献。
