Expression and Functional Analysis of Recombinant Human Lactoferrin

Abstract

Lactoferrin is a multifunctional iron-binding glycoprotein with potent antimicrobial properties. The protein is a prominent component of human milk, and also is found in most other exocrine secretions and in neutrophil granulocyte cells. Exploitation of the human protein as a natural antibiotic has not been feasible to date owing to the lack of a cost-effective means to produce sufficient quantities of purified lactoferrin. Previously, we reported the production of limited quantities of biologically active recombinant human lactoferrin in the filamentous fungus, Aspergillus oryzae. In the present study, we report a modification of this production system combined with a classical strain improvement program that has enabled production of levels of recombinant human lactoferrin in excess of 2 g/L. The protein was expressed in Aspergillus awamori as a glucoamylase fusion polypeptide that was secreted into the growth medium and processed to mature human lactoferrin by an endogenous KEX-2 peptidase. The recombinant protein retains full biological activity in terms of its ability to bind iron and human enterocyte receptors. Furthermore, the recombinant protein functions as a potent broad-spectrum antimicrobial protein.