Abstract: Bile salts (BSs) are amphipathic molecules, essential for absorption of dietary fats and excretion of metabolites and drugs. The BSs pool of the body is maintained through a recycling process called the enterohepatic circulation. Na+-taurocholate co-transporting polypeptide (NTCP), members of the solute carrier 10 (SLC10) family, facilitates the BS uptake in to liver from blood, and is a critical component of this bile acid homeostasis system. Interestingly, NTCP is also the receptor of human hepatitis B and D viruses’ (HBV/HDV) entry into hepatocytes. This interaction with virion, Liver specific expression and potential to influence cholesterol levels makes NTCP an important target for hepatitis B/D treatment, cholesterol lowering therapies and targeted delivery of drugs to liver. However, the mechanisms of NTCP transport and its interaction with the virus are incompletely understood. In this study, motivated with the lack of the structural information on human NTCP function, we used cryo-electron microscopy (cryo-EM) and conformation-specific nanobodies (Nbs) to decipher key conformations of NTCP transport cycle. We determined structure of human NTCP in complexes with two nanobodies, Nb87 and Nb91. Nb91 stabilizes NTCP in an unexpected conformation with a wide transmembrane pore, revealing path for substrate transport and exposing key determinant residues for HBV/HDV binding to the extracellular surface. In contrast, Nanobody87 stabilizes closed-pore inward-facing state and inhibits binding of receptor-binding preS1 domain of HBV/HDV, thus revealing a selectivity of the viruses for binding to open-to-outside over inward-facing conformations. Our results provide new insights into NTCP “gated-pore” transport, and HBV/HDV receptor-recognition mechanisms, and should help uncovering NTCP pharmacological potential in treatment of liver diseases.

Meeting ID: 930 7442 7095
Passcode: 110211