Diversity of Globin Function: Enzymatic, Transport, Storage, and Sensing

The availability of genomic information from the three kingdoms of life has altered substantially our view of the globin superfamily. It is now evident that Hbs,2 defined as hemeproteins comprising five to eight α-helices (A–H), with an invariant His at position F8 providing the proximal ligand to the heme iron, occur as three families in two structural classes (1). Within each family, the Hb can be either chimeric or SD. Historically, the first members of the two families that display the canonical 3/3 α-helical fold were chimeric: the FHbs in Escherichia coli and yeast discovered in ∼1990, consisting of an N-terminal Hb coupled to a ferredoxin reductase-like domain, and the GCSs reported in bacteria and Archaea a decade later, comprising an N-terminal Hb linked to variable gene regulatory domains.