| Bacterioferritin, also known as cytochrome B1, is an iron storage protein of obligate and facultative aerobic prokaryotes. Bacterioferritin (Bfr) has been isolated from many bacteria including, Escherichia coli , Azotobacter vinelendii, Azotobacter chroococcum and Pseudomonas aeruginosa (3,4). Electron microscopy, amino acid sequence alignment, x-ray diffraction and secondary structure determination. experiments have all indicated that E. coli Bfr has a very similar structure to human ferritin. The molecular model proposed for E. coli Bfr shows a typical ferritin related 4-alpha-helical bundle subunit. The Bfr of E. coli contains 24 identical subunits with usually 3-11 heme groups associated with each molecule but up to 12 is possible. This is the first structure of a bis-methionine ligated heme-binding site and the first case of a twofold symmetric binding site (2,3,4). In the proposed model of E. coli Bfr there are two types of hydrophobic pockets within which two methionine residues are directly responsible for binding heme. It has also been suggested that E. coli Bfr posses a ferroxidase center. If this ferroxidase center exists it is quite possible that Fe(III) ions may reside at or near this ferroxidase center. |
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Caleb W. Dorsey
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