H5N1 highly pathogenic
avian influenza virus (HPAIV) poses a huge threat to public health and the global economy. These viruses cause systemic
infection in poultry and accidental human
infection leads to severe
pneumonia, associated with high mortality rates. The
hemagglutinin (HA) of H5N1 HPAIV possesses multiple
basic amino acids, as in the sequence RERRRKKR at the cleavage site; however, the role of this motif is not fully understood. Here, we showed that a 33-amino
acid long
peptide derived from HA of H5N1 HPAIV (HA314-46) has the potential to penetrate various cells and lung tissue through a
sialic acid-independent endocytotic pathway. Mutant
peptide analyses revealed that the
cysteine residue at position 318 and multiple
basic amino acids were essential for the cell-penetrating activity. Moreover, reassortant viruses possessing H5 HA could enter
sialic acid-deficient cells, and virus internalisation was facilitated by cleavage with recombinant
furin. Thus, our findings demonstrate that the HA314-46 motif exhibits cell-penetrating activity through a
sialic acid-independent cell entry mechanism.