Scientists studied the blood clam Anadara granosa and found it has 31 different globin genes, many created by gene duplication. They discovered two new ancient globin groups and saw that these proteins may have been attached to cell membranes through myristoylation and palmitoylation. The research suggests that early animals had a richer set of globin genes than we thought, and that changes in protein structure helped hemoglobin evolve to carry oxygen better.

In recent decades, various globin groups have been identified and characterized in vertebrates, while studies on invertebrates remain limited. Therefore, we conducted this study to explore the repertoire, evolution, and functions of globin genes in the blood clam Anadara granosa, an economically significant bivalve known for its hemoglobin. A total of 31 globin genes were identified, driven by tandem gene duplications that played a pivotal role in their expansion. Phylogenetic analysis identifies two previously unreported basal clades, provisionally named cluster A and B, alongside the well-known ancient globin groups neuroglobin, androglobin, globin X, and globin X-like. This suggests that invertebrates may have retained a more complete ancestral globin gene repertoire compared to vertebrates, and that the globin gene repertoire in the last common ancestor of vertebrates and invertebrates was more diverse than previously hypothesized. Protein structural analyses indicate that evolutionary changes in hemoglobin's oxygen-transport function may be driven by structural alterations in the CD region and EF helices or substitutions at select residues therein. Furthermore, the ancient globin groups exhibit widespread N-myristoylation and 3C-palmitoylation modifications, indicating their potential membrane-associated ancestral functions. Transcriptome analysis and hypoxia stress experiments indicate that globins are involved in the development and hypoxia tolerance of A. granosa. The pentacoordinate heme in animal globins likely switched from a hexacoordinate form, possibly associated with the evolution of oxygen-carrying functionality. This study expands our understanding of the globin superfamily's structure, function, and evolution, particularly in mollusks.