The Study On The Structure And Function Of Mpef

Iron plays an important role in all kings of life processes,but it is extremely poisonous for living organisms,so it needs regulation.Ferritins are unique iron storage protein and detoxification protein,which has the characteristics of highly conserved structure,strong stability,can participate in iron regulation.The hot researches of ferritin mainly focus on the mechanism of iron oxidation,iron uptake and iron nucleation.So far,most animals,plants and bacterial ferritin have been deeply studied,but the reports of ferritin from Mycoplasma are rare.Mycoplasma is one of the minimal prokaryotic self-replicating micro-organism with no cell wall.Its size is0.1-0.3 ?m.Mycoplasma penetrans is a kind of Mycoplasma associated with AIDS,which can adhere to and penetrate eukaryotic cell membranes.At present,the structure of any mycoplasma ferritin has not been resolved yet.In this paper,the crystallographic study of mycoplasma penetrans ferritin was carried out,and results are as follow:1.The crystal of Mpef was analyzed,which was the first Mycoplasma ferritin with a resolution of 1.9 (?).The cage structure of Mpef consists of 24 subunits without heme.Therefore,Mpef is clearly different from bacterial ferritin.2.The crystal structure showed that the amino acid residues composed of ferroxidase center of Mpef were all from B and D helices,which was a new ferroxidase center.The iron binding sites A and B of the ferroxidase center in Mpef bind to one iron atom respectively at a distance of 2.9 (?).The iron atom in site A coordinates amino acid residues D55,H60,D134,D138 and two water molecules,and the iron atom in site B coordinates amino acid residues D138,E141 and four water molecules.The C-terminal of Mpef is invisible in the crystal structure,and the results of molecular dynamic simulation show that this region consists of all negatively charged amino acid residues and may be involved in the composition of the site C in ferroxidase center.3.Ferric ions enter the ferroxidase center of Mpef through the hydrophilic B channel,and the residue E141 connects the B channel and ferroxidase center to transfer ferric ions.The 3-fold axis of Mpef are hydrophobic channel,and the 4-fold channel is hydrophilic channel,but it does not participate in the ferric ions uptake process.4.The low activity of Mpef ferroxidase center was possibly mainly attributed to the structure of active site,the ferrous ion uptake channel and the amino acid residues outside the active site.