Divergence of the F1-ATP Synthase Complex in the Ice Worm, Mesenchytraeus solifugus (Annelida, Clitellata, Enchytraeidae)

Abstract

The F 1 -ATP synthase complex constitutes the catalytic component of F 1 F 0 -ATP synthase, the primary ATP synthetic enzyme in the cell. Previous studies indicate that the glacier ice worm, Mesenchytraeus solifugus, maintains unusually high ATP levels that continue to rise as temperatures decline, suggesting that molecular changes within ice worm F 1 -ATP synthase subunits may contribute to this energetic anomaly. In this report, we compared ice worm F 1 -ATP synthase subunits (a, b, c) with homologues across metazoan phyla (arthropod, chordate, nematode) and among a group of clitellate annelids (Enchytraeus albidus, Enchytraeus buchholzi, Lumbriculus variegatus, Theromyzon tessulatum). Amino acid alignments indicated that ice worm F 1 -ATP a and F 1 -ATP b subunits share strong sequence homology with their mesophilic counterparts, respectively, but that ATP c has diverged more rapidly. Moreover, F 1 -ATP a and F 1 -ATP b displayed amino acid compositional changes consistent with trends observed in other cold adapted proteins, while F 1 -ATP c diverged in unexpected directions (e.g., gains in size, charged residues). Several ice worm-specific amino acid substitutions map to positions near the F 1 -ATP b catalytic site while others occur near subunit contact sites.