Distinct structural characteristics define a new subfamily of Mycoplasma ferritin

Ferritins can generally be divided into four subfamilies based on their structural characteristics, namely, the classic ferritins (Ftns), bacterioferritins (Bfrs), DNA-binding proteins from starved cells (Dps’), and encapsulated ferritins (EncFtns). However, the ferritin from Mycoplasma penetrans (Mpef) possesses a particular ferroxidase center with an extreme low activity and exhibits unusual characteristics, indicating that it could be a member of a quite different subfamily of ferritins. Hereby, the crystal structure of the ferritin from Ureaplasma urealyticum (Uurf) is presented, Mpef and Uurf have very similar properties, though they display very low sequence similarity. Thus, ferritins from Mycoplasma with these unique properties do not belong to any known subfamily, but they should rather be placed in a novel ferritin subfamily, which we term Mycoplasma Ferritin (Mfr). Ferritin from Mycoplasma represents some unique characteristics, including a unique ferroxidase center and much lower iron oxidation activity, as well as the channel for iron passthrough. Therefore, it should be classified into a new ferritin subfamily, Mycoplasma ferritin (Mfr).