Expression and characterization of recombinant murine lactoferrin.

Lactoferrin (Mw=78 kDa) is a member of the transferrin family of iron-binding glycoproteins. Previous studies carried out primarily in vitro indicate that the protein has multifunctional properties and may be involved in regulation of iron homeostasis, inhibition of bacterial growth and regulation of immune responses. However, the significance and species specificity of these proposed functions in vivo have not been adequately addressed due to lack of sufficient purified homospecies lactoferrin for analysis in small animal models. We previously reported the successful production of biologically active recombinant human lactoferrin using an Aspergillus expression system. In the present study, we report the production of recombinant murine lactoferrin using a similar expression strategy. Recombinant murine lactoferrin was purified to homogeneity and was similar in size and immunoreactivity to native murine milk lactoferrin. The recombinant protein was correctly processed at its N-terminus and was glycosylated. Interestingly, while both human and murine lactoferrin bind iron in a 2:1 molar ratio, iron bound to recombinant murine lactoferrin was more acid labile than human lactoferrin, demonstrating species-specific variation in the stability of iron-binding to this protein. Finally, the availability of recombinant murine lactoferrin will now facilitate the study of the species specificity of lactoferrin action in a mouse model system.