N-Terminal AH2 segment of protein NS4B from hepatitis C virus. Binding to and interaction with model biomembranes

HCV NS4B, a highly hydrophobic protein involved in the alteration of the intracellular host membranes forming the replication complex, plays a critical role in the HCV life cycle. NS4B is a multifunctional membrane protein that possesses different regions where diverse and significant functions are located. One of these important regions is the AH2 segment, which besides being highly conserved has been shown to play a significant role in NS4B functioning. We have carried out an in-depth biophysical study aimed at the elucidation of the capacity of this region to interact, modulate and disrupt membranes, as well as to study the structural and dynamic features relevant for that disruption. We show that a peptide derived from this region, NS4B_AH2, is capable of specifically binding phosphatidyl inositol phosphates with high affinity, and its interfacial properties suggest that this segment could behave similarly to a pre-transmembrane domain partitioning into and interacting with the membrane depending on the membrane composition and/or other proteins. Moreover, NS4B_AH2 is capable of rupturing membranes even at very low peptide-to-lipid ratios and its membrane-activity is modulated by lipid composition. NS4B_AH2 is located in a shallow position in the membrane but it is able to affect the lipid environment from the membrane surface down to the hydrophobic core. The NS4B region where peptide NS4B_AH2 resides might have an essential role in the membrane replication and/or assembly of the viral particle through the modulation of the membrane structure and hence the replication complex.