The loss of the hemoglobin H2S-binding function in annelids from sulfide-free habitats reveals molecular adaptation driven by Darwinian positive selection.

摘要: The hemoglobin of the deep-sea hydrothermal vent vestimentiferan Riftia pachyptila (annelid) is able to bind toxic hydrogen sulfide (H2S) free cysteine residues and transport it fuel endosymbiotic sulfide-oxidising bacteria. are conserved key amino acids in annelid globins living sulfide-rich environments, but absent from sulfide-free environments. Synonymous nonsynonymous substitution analysis two different sets orthologous globin genes rich environments have been performed understand how sulfide-binding function appeared has maintained during course evolution. This study reveals that sites occupied by free-cysteine annelids other undergone positive selection We assumed high reactivity became a disadvantage when H2S disappeared because cysteines without their natural ligand had capacity interact with blood components, disturb homeostasis, reduce fitness thus could counterselected. To our knowledge, we pointed out for first time case loss driven molecular adaptation rather than genetic drift. If constraint relaxation (H2S disappearance) led modern work suggests plesiomorphic feature, ancestor emerged environment.