Structure and function evolution in the superfamily of globins

The superfamily of globins has emerged some 4000 Myr from a common ancestor, which was among the basic protein components required for life. Globins are present in the three kingdoms of life. From a structure point of view, these molecules are defined by the presence of a characteristic protein fold, rich in alpha-helix, surrounding a heme group. Depending on the species or organs, they may be physiologically active as monomers, tetramers or large size polymers. Their function varies from the classical reversible binding of oxygen for transport and storage to cytoprotection against reactive oxygen species, NO scavenging, signaling in oxygen dependent metabolic pathways, or possibly other specific properties involving ligand or electron transfer. All these aspects are discussed in this review.