Analyzing the functional divergence of Slo1 and Slo3 channel subfamilies

Slo1 and Slo3 encode close paralogues of the Slo potassium (K⁺) channels family. Despite their evolutionary relatedness, Slo1 and Slo3 channels show marked functional differences and evolutionary dynamics. Whereas Slo1 is a highly conserved and widely expressed channel, Slo3 is a rapidly evolving channel restricted to sperm. However, the molecular mechanisms behind the structural-functional differences of Slo1 and Slo3 channels are unknown. In this study, we explored the functional divergence of Slo1 and Slo3 subfamilies in vertebrates and examined the structure-function relationships of our predictions using experimental data. We found that ∼25% of sites between Slo1 and Slo3 underwent altered functional constraints, affecting some residues with important roles in Slo1 channel gating. Because functional divergence was principally generated by accelerated evolution of Slo3 after gene duplication, we explored selective forces behind Slo3 diversification. We observed that Slo3 subjected was principally subjected to relaxation of purifying selection, but we also identified several sites evolving under positive selection in the cytosolic domain of this channel . Concerning Slo1, this channel presented strong purifying selection. Whether residues evolving under different selection in Slo1 and Slo3 are responsible for functional differences observed between these channels, as well as among Slo3 orthologs, remains to be established.