Schematic representation of the HBD region (green) based on the previously reported crystal structure of dimeric NS5A domain I (Tellinghuisen et al., 2005). A. NS5A domain I dimer. B. The HBD hairpin moiety shown at two different angles. The side chains of four conserved residues (Phe171, Val173, Leu175, and Tyr178) are also shown. C. The HBD hairpin moiety showing four additional residues in blue (Thr170, Leu172, Gln177 and Leu179) that were substituted with arginine residues to enhance cell permeability of HCV peptides.