Bioinformatic Characterization and Molecular Evolution of the Lucina pectinata Hemoglobins

(1) Introduction: is a clam found in sulfide-rich mud environments that has three hemoglobins believed to be responsible for the transport of hydrogen sulfide (HbI ) and oxygen (HbII and HbIII ) to chemoautotrophic endosymbionts. The physiological roles and evolution of these globins in sulfide-rich environments are not well understood. (2) Methods: We performed bioinformatic and phylogenetic analyses with 32 homologous mollusk globin sequences. Phylogenetics suggests a first gene duplication resulting in sulfide binding and oxygen binding genes. A more recent gene duplication gave rise to the two oxygen-binding hemoglobins. Multidimensional scaling analysis of the sequence space shows evolutionary drift of HbII and HbIII , while HbI was closer to the hemoglobins. Further corroboration is seen by conservation in the coding region of hemoglobins from compared to those from . (3) Conclusions: Presence of glutamine in position E7 in organisms living in sulfide-rich environments can be considered an adaptation to prevent loss of protein function. In HbI a substitution of phenylalanine in position B10 is accountable for its unique reactivity towards H S. It appears that HbI has been changing over time, apparently not subject to functional constraints of binding oxygen, and acquired a unique function for a specialized environment.