Department of Pathology, Emory School of Medicine, Atlanta, GA 30322, USA.
Proc Natl Acad Sci U S A. 2011 Nov 1;108(44):18162-7. doi: 10.1073/pnas.1115405108. Epub 2011 Oct 17.
Fogel and Hastings first hypothesized the existence of voltage-gated proton channels in 1972 in bioluminescent dinoflagellates, where they were thought to trigger the flash by activating luciferase. Proton channel genes were subsequently identified in human, mouse, and Ciona intestinalis, but their existence in dinoflagellates remained unconfirmed. We identified a candidate proton channel gene from a Karlodinium veneficum cDNA library based on homology with known proton channel genes. K. veneficum is a predatory, nonbioluminescent dinoflagellate that produces toxins responsible for fish kills worldwide. Patch clamp studies on the heterologously expressed gene confirm that it codes for a genuine voltage-gated proton channel, kH(V)1: it is proton-specific and activated by depolarization, its g(H)-V relationship shifts with changes in external or internal pH, and mutation of the selectivity filter (which we identify as Asp(51)) results in loss of proton-specific conduction. Indirect evidence suggests that kH(V)1 is monomeric, unlike other proton channels. Furthermore, kH(V)1 differs from all known proton channels in activating well negative to the Nernst potential for protons, E(H). This unique voltage dependence makes the dinoflagellate proton channel ideally suited to mediate the proton influx postulated to trigger bioluminescence. In contrast to vertebrate proton channels, whose main function is acid extrusion, we propose that proton channels in dinoflagellates have fundamentally different functions of signaling and excitability.
1972 年，Fogel 和 Hastings 首次在生物发光甲藻中假设存在电压门控质子通道，他们认为这些质子通道通过激活荧光素酶来触发闪光。随后在人类、小鼠和海鞘中鉴定出质子通道基因，但在甲藻中它们的存在仍未得到证实。我们根据已知质子通道基因的同源性，从 Karlodinium veneficum cDNA 文库中鉴定出一个候选质子通道基因。K. veneficum 是一种捕食性的非生物发光甲藻，它产生的毒素是导致全球鱼类死亡的罪魁祸首。对异源表达基因的膜片钳研究证实，它编码一种真正的电压门控质子通道 kH(V)1：它是质子特异性的，可被去极化激活，其 g(H)-V 关系随外部或内部 pH 值的变化而变化，并且选择性过滤器（我们鉴定为 Asp(51)）的突变导致质子特异性传导丧失。间接证据表明，kH(V)1 是单体的，与其他质子通道不同。此外，kH(V)1 在激活方面与所有已知的质子通道不同，其激活电位远低于质子的 Nernst 电位，E(H)。这种独特的电压依赖性使甲藻质子通道非常适合介导被假设为触发生物发光的质子内流。与主要功能为酸外排的脊椎动物质子通道不同，我们提出甲藻中的质子通道具有信号转导和兴奋性的根本不同功能。
