Evolution of Inverted Repeats in Membrane Transporters

Abstract

The majority of membrane transport proteins of known structure exhibit internal repeat symmetry, with two or more structurally homologous domains. inverted repeat architecture, where the domains are antiparallel with respect to each other, is especially common. This architecture implies the existence of ancestral monomeric proteins that form dual-topology antiparallel dimers, before duplication and fusion led to the extant inverted repeat forms. The Fluc family of fluoride channels is the first family to be discovered that connects these two evolutionary extremes, with both dual topology and inverted repeat representatives. Here we use the Fluc family of fluoride channels to model genetic drift in a newly duplicated membrane protein. Using fluoride resistance assays, we pursue a deep mutational scan to describe how evolutionary forces like mutational robustness and paralogue interference play out after the duplication of single-domain membrane proteins. We connect these experiments to phylogenetic observations of the Fluc superfamily.