PROSITE documentation PDOC00793

Globin family profile

Globins are heme-containing proteins involved in binding and/or transporting oxygen [1]. They belong to a very large and well studied family which is widely distributed in many organisms. The major groups of globins are:

• Hemoglobins (Hb) from vertebrates. Hb is the protein responsible for transporting oxygen from the lungs to other tissues. It is a tetramer of two α and two β chains. Most vertebrate species also express specific embryonic or fetal forms of hemoglobin where the α or the β chains are replaced by a chain with higher oxygen affinity, as for the γ, delta, epsilon and zeta chains in mammals, for example.
• Myoglobins (Mg) from vertebrates. Mg is a monomeric protein responsible for oxygen storage in muscles.
• Invertebrate globins [2]. A wide variety of globins are found in invertebrates. Molluscs generally have one or two muscle globins which are either monomeric or dimeric. Insects, such as the midge Chironomus thummi, have a large set of extracellular globins. Nematodes and annelids have a variety of intracellular and extracellular globins; some of them are multi- domain polypeptides (from two up to nine-domain globins) and some produce large, disulfide-bonded aggregates.
• Leghemoglobins (Lg) from the root nodules of leguminous plants. Lg provides oxygen for bacteroids.
• Flavohemoproteins from bacteria (Escherichia coli hmpA) and fungi. These proteins consist of two distinct domains: an N-terminal globin domain and a C-terminal FAD-containing reductase domain. In bacteria such as Vitreoscilla, the enzyme-associated globin is a single domain protein.

All these globins seem to have evolved from a common ancestor. The profile developed to detect members of the globin family is based on a structural alignment of selected globin sequences.