Bovine and human lactoferrins (LF) prevent hepatitis C virus (HCV)
infection in cultured human hepatocytes; the preventive mechanism is thought to be the direct interaction between LF and HCV. To clarify this hypothesis, we have characterized the binding activity of LF to HCV E2 envelope
protein and have endeavored to determine which region(s) of LF are important for this binding activity. Several regions of human LF have been expressed and purified as
thioredoxin-fused
proteins in Escherichia coli. Far-Western blot analysis using these LF fragments and the E2
protein, expressed in Chinese hamster ovary cells, revealed that the 93 carboxyl
amino acids of LF specifically bound to the E2
protein. The 93 carboxyl
amino acids of LFs derived from bovine and horse cells also possessed similar binding activity to the E2
protein. In addition, the amino acid sequences of these carboxyl regions appeared to show partial homology to CD81, a candidate receptor for HCV, and the binding activity of these carboxyl regions was also comparable with that of CD81. Further deletion analysis identified 33
amino acid residues as the minimum binding site in the carboxyl region of LF, and the binding specificity of these 33
amino acids was also confirmed by using 33
maltose-binding protein-fused
amino acids. Furthermore, we demonstrated that the 33
maltose-binding protein-fused
amino acids prevented HCV
infection in cultured human hepatocytes. In addition, the site-directed mutagenesis to an Ala residue in both terminal residues of the 33
amino acids revealed that Cys at
amino acid 628 was determined to be critical for binding to the E2
protein. These results led us to consider the development of an effective anti-HCV
peptide. This is the first identification of a natural
protein-derived
peptide that specifically binds to HCV E2
protein and prevents HCV
infection.