The Globin Gene Family
The HBB gene is classified in the globin gene family. The Globin gene family consists of proteins which contain 8 alpha helical segments which bind heme and are associated with reversible oxygen binding and transport (Pfam Globin PF00042). There are 2 main types of globins which span the three kingdoms of life (Bacteria, Archaea and Eukaryotes): single domain globins and two types of chimeric globins (Vinogradov et al., 2006; Vinogradov et al., 2007). Flavohaemoglobins and globin coupled sensors comprise the types of globin molecules found in the chimeric globins group. Bacteria utilize all 3 types of globins, while organisms in the archaea group use single domain globins and globin coupled sensors. Eukaryotes make use of the Flavohaemoglobins and single domain globins (Vinogradov et al., 2006). Flavohaemoglobins are said to give unicellular organisms protection again nitric oxide and other reactive nitrogen species (Mukai et al., 2001). Globin coupled sensors are said to be chimeric two domain regulators containing heme that were found to be involved in gene or aerotactic regulation (Freitas et al, 2005). Proteoglobins are a group of globin coupled sensors that have been proposed as the ancestral globin molecule (Vinogradov et al., 2006).