Convergent Evolution of Sodium Ion Selectivity in Metazoan Neuronal Signaling

• Main Authors: Maya Gur Barzilai, Adam M. Reitzel, Johanna E.M. Kraus, Dalia Gordon, Ulrich Technau, Michael Gurevitz, Yehu Moran
• Format: Article
• Language: English
• Published: Elsevier 2012-08-01
• Series: Cell Reports
• Online Access: http://www.sciencedirect.com/science/article/pii/S2211124712001908

Ion selectivity of metazoan voltage-gated Na+ channels is critical for neuronal signaling and has long been attributed to a ring of four conserved amino acids that constitute the ion selectivity filter (SF) at the channel pore. Yet, in addition to channels with a preference for Ca2+ ions, the expression and characterization of Na+ channel homologs from the sea anemone Nematostella vectensis, a member of the early-branching metazoan phylum Cnidaria, revealed a sodium-selective channel bearing a noncanonical SF. Mutagenesis and physiological assays suggest that pore elements additional to the SF determine the preference for Na+ in this channel. Phylogenetic analysis assigns the Nematostella Na+-selective channel to a channel group unique to Cnidaria, which diverged >540 million years ago from Ca2+-conducting Na+ channel homologs. The identification of Cnidarian Na+-selective ion channels distinct from the channels of bilaterian animals indicates that selectivity for Na+ in neuronal signaling emerged independently in these two animal lineages.