Structural Evolution of the Glacier Ice Worm F_o ATP Synthase Complex

The segmented annelid worm, Mesenchytraeus solifugus, is a permanent resident of temperate, maritime glaciers in the Pacific northwestern region of North America, displaying atypically high intracellular ATP levels which have been linked to its unusual ability to thrive in hydrated glacier ice. We have shown previously that ice worms contain a highly basic, carboxy terminal extension on their ATP6 regulatory subunit, likely acquired by horizontal gene transfer from a microbial dietary source. Here we examine the full complement of F₁F₀ ATP synthase structural subunits with attention to non-conservative, ice worm-specific structural modifications. Our genomics analyses and molecular models identify putative proton shuttling domains on either side of the F₀ hemichannel, which predictably function to enhance proton flow across the mitochondrial membrane. Other components of the ice worm ATP synthase complex have remained largely unchanged in the context of Metazoan evolution.