An Insect Proton Channel

Abstract

Voltage-gated proton channels have been identified in a wide range of eukaryotes. The channel is an important component of the cellular proton extrusion machinery and is essential for charge compensation during the respiratory burst of phagocytes. Especially in the animal kingdom voltage gated proton channels can be found consistently. However, most insect genomes analyzed so far seems to be deprived of voltage-gated proton channels. Therefore, it has been proposed that insects do not possess voltage-gated proton channels, although until recently mainly dipteran insect genomes were sequenced. Despite this long standing dogma, here we report the discovery of voltage-gated proton channels in insects. We have performed a comprehensive search in insect TSA data bases and found putative Hv homologs in basal insects and various polyneopteran species. As a prototype insect Hv channel, the proton channel of the zygentoma Nicoletia phytophila (NpHV1) is composed of 239 amino acids with protein identity of 33% to the human proton channel hHV1. Patch clamp measurements in a heterologous expression system showed proton selectivity, pH dependent and voltage dependent gating. Interestingly, NpHv1 shows a slightly enhanced pH dependent gating compared to the human channel. Mutations at position 66 (Asp66), the presumed selectivity filter, lead to a loss of proton-selective conduction, confirming the importance of the aspartate in the first transmembrane segment in all voltage-gated proton channels.