Globins are heme-containing proteins involved in binding and/or transporting
oxygen . 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 . 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.
Protozoan/cyanobacterial globins belong to another family which is
described in <PDOC00933>.
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