Unification of the ferritin family of proteins.

Ferritin is the iron-storage protein of eukaryotic organisms. The nucleotide sequence encoding Azotobacter vinelandii bacterioferritin, a hemoprotein, was determined. The deduced amino acid sequence reveals a high degree of identity with Escherichia coli bacterioferritin and a striking similarity to eukaryotic ferritins. Moreover, derivation of a global alignment shows that virtually all key residues specifying the unique structural motifs of eukaryotic ferritin are conserved or conservatively substituted in the A. vinelandii sequence. The alignment suggests specific methionine residues as heme-binding ligands in bacterioferritins. The overall sequence similarity with conservation of key structural residues implies that all ferritins form a unified family of proteins. The results implicate ferritins as proteins potentially common to all aerobic organisms and as such useful in taxonomic classification, evolutionary analysis, and environmental monitoring.