K2P channels in plants and animals

Two-pore domain potassium (K-2P) channels are membrane proteins widely identified in mammals, plants, and other organisms. A functional channel is a dimer with each subunit comprising two pore-forming loops and four transmembrane domains. The genome of the model plant Arabidopsis thaliana harbors five genes coding for K-2P channels. Homologs of Arabidopsis K-2P channels have been found in all higher plants sequenced so far. As with the K-2P channels in mammals, plant K-2P channels are targets of external and internal stimuli, which fine-tune the electrical properties of the membrane for specialized transport and/or signaling tasks. Plant K-2P channels are modulated by signaling molecules such as intracellular H+ and calcium and physical factors like temperature and pressure. In this review, we ask the following: What are the similarities and differences between K-2P channels in plants and animals in terms of their physiology? What is the nature of the last common ancestor (LCA) of these two groups of proteins? To answer these questions, we present physiological, structural, and phylogenetic evidence that discards the hypothesis proposing that the duplication and fusion that gave rise to the K-2P channels occurred in a prokaryote LCA. Conversely, we argue that the K-2P LCA was most likely a eukaryote organism. Consideration of plant and animal K-2P channels in the same study is novel and likely to stimulate further exchange of ideas between students of these fields.