Multitasking Na+/Taurocholate Cotransporting Polypeptide (NTCP) as a Drug Target for HBV Infection: From Protein Engineering to Drug Discovery

Abstract

Hepatitis B virus (HBV) infections are among the major public health concerns worldwide with more than 250 million of chronically ill individuals. Many of them are additionally infected with the Hepatitis D virus, a satellite virus to HBV. Chronic infection frequently leads to serious liver diseases including cirrhosis and hepatocellular carcinoma, the most common type of liver cancer. Although current antiviral therapies can control HBV replication and slow down disease progress, there is an unmet medical need to identify therapies to cure this chronic infectious disease. Lately, a noteworthy progress in fighting against HBV has been made by identification of the high-affinity hepatic host receptor for HBV and HDV, namely Na+/taurocholate cotransporting polypeptide (NTCP, gene symbol SLC10A1). Next to its primary function as hepatic uptake transporter for bile acids, NTCP is essential for the cellular entry of HBV and HDV into hepatocytes. Due to this high-ranking discovery, NTCP has become a valuable target for drug development strategies for HBV/HDV-infected patients. In this review, we will focus on a newly predicted three-dimensional NTCP model that was generated using computational approaches and discuss its value in understanding the NTCP’s membrane topology, substrate and virus binding taking place in plasma membranes. We will review existing data on structural, functional, and biological consequences of amino acid residue changes and mutations that lead to loss of NTCP’s transport and virus receptor functions. Finally, we will discuss new directions for future investigations aiming at development of new NTCP-based HBV entry blockers that inhibit HBV tropism in human hepatocytes.

Tyrosine 146 of the Human Na+/Taurocholate Cotransporting Polypeptide (NTCP) Is Essential for Its Hepatitis B Virus (HBV) Receptor Function and HBV Entry into Hepatocytes

“…Although, during revision of the manuscript, three independent cryo-EM structures of human NTCP were published [13][14][15], partly with bound viral myr-preS1 peptide, the precise molecular interactions between the host-derived NTCP receptor and the HBV surface proteins are still not fully understood. Experimental approaches, such as protein engineering and computational biology methods, are powerful tools in exploring motifs within the NTCP protein that are essential for regulation of its HBV affinity during infection [3,9,10,12,23,24,32,33]. In this study, we identified a novel NTCP tyrosine-enriched motif 139YIYSRGIY146 that is significantly involved in the regulation of NTCP-HBV preS1 interactions and, thus, in the control of NTCP receptor function (Figure 7A,B).…”

“…To date, little is known about the mechanistic insights into the process of initial NTCP-HBV complex assembly and NTCP-mediated virus entry into hepatocytes [9,10]. Although, during revision of the manuscript, three independent cryo-EM structures of human NTCP were published [13][14][15], partly with bound viral myr-preS1 peptide, the precise molecular interactions between the host-derived NTCP receptor and the HBV surface proteins are still not fully understood.…”

“…Protein surface-exposed regions of NTCP play an essential role during initial docking of HBV to hepatocytes [35]. Until now, only few such motifs have been identified and characterized giving prerequisites for the prediction of preS1-NTCP interactions taking place upon HBV infection [6,9,10]. It seems that different NTCP motifs are required for high-affinity virus binding and entry into hepatocytes, such as 84RLKN87, 157KGIVISLVL165, S267, and N5/N11 [6,9,10].…”

“…Although NTCP-dependent HBV infection has received much attention over the last decade, the precise molecular sites of the virus/NTCP interaction have not been fully identified [9,10]. Nonetheless, some molecular determinants that are important for virus attachment to NTCP/Ntcps of different species have already been reported [3,4,[10][11][12].…”

“…Although NTCP-dependent HBV infection has received much attention over the last decade, the precise molecular sites of the virus/NTCP interaction have not been fully identified [9,10]. Nonetheless, some molecular determinants that are important for virus attachment to NTCP/Ntcps of different species have already been reported [3,4,[10][11][12]. For instance, a small motif containing residues 84RLKN87 in human NTCP and 84HLTS87 in mouse Ntcp is essential for HBV infection in humans, but restricts infection in cells expressing the mouse Ntcp.…”