Gating Differs Between an Antarctic and a Tropical Kv1 Channel Because of RNA Editing

Abstract

In squid, shaker-like potassium channel mRNA's are extensively edited by adenosine deamination. Because A-to-I RNA editing tends to recode for smaller amino acids, it could create more flexible proteins and be involved in cold adaptation. In this study we compare editing patterns and their functional consequences for a Kv1 K+ channel mRNA from two species of octopus: Pareledone sp., from the extreme cold of Antarctica and O. vulgaris from tropical inshore waters of Puerto Rico. From each species, the same Kv1 gene was cloned and sequenced. An editing map was created by sequencing 50 cDNA clones and identifying sites with A/G variation. At the genomic level, the channels were nearly identical, differing by four amino acids. By contrast, their editing patterns differed substantially. In total there were 13 non-silent editing sites, with five sites unique to one species or the other. At four sites editing percentages differed by more than 50% between species: N40S and S54G are edited more in O. vulgaris while N105G and I321V are edited more in Pareledone. We tested the eletrophysiological effects of differences at both the genomic and RNA editing levels. Channels were expressed in Xenopus oocytes and their kinetics of activation, deactivation, and inactivation, along with their voltage-dependence, were compared. The two genomically encoded channels were nearly identical, although the activation kinetics were slightly faster for the Antarctic channel. Individual editing sites, however, changed multiple parameters. The “tropical” edits N40S and S54G, both in the tetramerization domain, slowed activation and accelerated inactivation. The “Antarctic” edit I321V shifted the voltage dependence of activation by +12 mV and more than doubled the rate of deactivation. I321V, which is in the S5 helix, appears to be a candidate for cold-adaptation.