EXPRESSION AND CHARACTERIZATION OF HUMAN LACTOFERRIN IN YEAST SACCHAROMYCES-CEREVISIAE

Lactoferrin (LF) has certain chemical and biological properties that are significant to the dairy food industry. To study the relationship between protein structure and functionality of LF with the aim of increasing the thermostability of LF, we established a yeast system for heterologous expression of cloned human LF cDNA. Human LF was successfully synthesized in yeast cells by placing the cloned cDNA under the regulation of yeast chelatin promoter. Both human LF and yeast invertase secretion signal sequences were used to direct the secretion of recombinant human LF synthesized in yeast cells. The construct of the expression unit containing the yeast invertase signal sequence resulted in relatively high levels of secretion of recombinant human LF (1.5-2.0 mg/L), whereas the other containing human LF secretion signal sequence produced quite low levels of secretion of the protein. The secreted recombinant human LF was purified from the yeast broth by heparin affinity and immunoaffinity chromatographies. The highly purified recombinant LF was confirmed to be bioactive, having iron-and copper-binding activities. Also, the recombinant LF synthesized in yeast was glycosylated. The levels of synthesis of human LF in the yeast system were not constant, and LF might be toxic to yeast cells.