Cytoglobin: a novel globin type ubiquitously expressed in vertebrate tissues.

Vertebrates possess multiple respiratory globins that differ in terms of structure, function, and tissue distribution. Three types of globins have been described so far: hemoglobin facilitates the transport of oxygen in the blood, myoglobin serves oxygen transport and storage in the muscle, and neuroglobin has a yet unidentified function in nerve cells. Here we report the identification of a fourth and novel type of globin in mouse, man, and zebrafish. It is expressed in apparently all types of human tissue and therefore has been called cytoglobin (CYGB). Mouse and human CYGBs comprise 190 amino acids; the zebrafish CYGB, 174 amino acids. The human CYGB gene is located on chromosome 17q25. The mammalian genes display a unique exon-intron pattern with an additional exon resulting in a C-terminal extension of the protein, which is absent in the fish CYGB. Phylogenetic analyses suggest that the CYGBs had a common ancestor with vertebrate myoglobins. This indicates that the vertebrate myoglobins are in fact a specialized intracellular globin that evolved in adaptation to the special needs of muscle cells.