Structure of recombinant human lactoferrin expressed in Aspergillus awamori

Human lactoferrin (hLf) has considerable potential as a therapeutic agent. Overexpression of hLf in the fungus Aspergillus awamori has resulted in the availability of very large quantities of this protein. Here, the three-dim ensional structure of the recombinant hLf has been determined by X-ray crys tallography at a resolution of 2.2 Angstrom. The final model, comprising 53 39 protein atoms (residues 1-691, 294 solvent molecules, two Fe3+ and two C O32- ions), gives an R factor of 0.181 (free R = 0.274) after refinement ag ainst 32231 reflections in the resolution range 10-2.2 Angstrom. Superposit ion of the recombinant hLf structure onto the native milk hLf structure sho ws a very high level of correspondence; the main-chain atoms for the entire polypeptide can be superimposed with an r.m.s. deviation of only 0.3 Angst rom and there are no significant differences in side-chain conformations or in the iron-binding sites. Dynamic properties, as measured by B-value dist ributions or iron-release kinetics, also agree closely. This shows that the structure of the protein is not affected by the mode of expression, the us e of strain-improvement procedures or the changes in glycosylation due to t he fungal system.