Evidence for Functional Diversity between the Voltage-Gated Proton Channel Hv1 and Its Closest Related Protein HVRP1

The Hv1 channel and voltage-sensitive phosphatases share with voltage-gated sodium, potassium, and calcium channels the ability to detect changes in membrane potential through voltage-sensing domains (VSDs). However, they lack the pore domain typical of these other channels. NaV, KV, and CaV proteins can be found in neurons and muscles, where they play important roles in electrical excitability. In contrast, VSD-containing proteins lacking a pore domain are found in non-excitable cells and are not involved in neuronal signaling. Here, we report the identification of HVRP1, a protein related to the Hv1 channel (from which the name Hv1 Related Protein 1 is derived), which we find to be expressed primarily in the central nervous system, and particularly in the cerebellum. Within the cerebellar tissue, HVRP1 is specifically expressed in granule neurons, as determined by in situ hybridization and immunohistochemistry. Analysis of subcellular distribution via electron microscopy and immunogold labeling reveals that the protein localizes on the post-synaptic side of contacts between glutamatergic mossy fibers and the granule cells. We also find that, despite the similarities in amino acid sequence and structural organization between Hv1 and HVRP1, the two proteins have distinct functional properties. The high conservation of HVRP1 in vertebrates and its cellular and subcellular localizations suggest an important function in the nervous system.

Hv1通道与电压敏感磷酸酶（voltage-sensitive phosphatases），同电压门控钠、钾及钙通道一样，均能通过电压感受结构域（voltage-sensing domains, VSDs）感知膜电位变化。不过二者缺乏上述其他通道所共有的典型孔结构域。电压门控钠（NaV）、钾（KV）及钙（CaV）蛋白可在神经元与肌肉中表达，在电兴奋性维持过程中发挥关键作用。与之相反，不含孔结构域的含VSD蛋白仅分布于非兴奋细胞，并不参与神经元信号传导。本研究报道了HVRP1的鉴定工作：该蛋白为Hv1通道的相关蛋白（其名称即源自Hv1 Related Protein 1）。我们发现其主要表达于中枢神经系统，尤以小脑组织中富集。经原位杂交与免疫组织化学实验验证，在小脑组织内，HVRP1特异性表达于颗粒神经元。通过电子显微镜与免疫金标记开展的亚细胞分布分析显示，该蛋白定位于谷氨酸能苔藓纤维与颗粒细胞之间接触位点的突触后侧。我们同时发现，尽管Hv1与HVRP1在氨基酸序列与结构组织上存在相似性，但二者的功能特性存在显著差异。HVRP1在脊椎动物中高度保守，结合其细胞与亚细胞定位特征，提示该蛋白在神经系统中具有重要生理功能。