Oligomerization of the HBV/HDV functional receptor NTCP expressed in Sf9 insect cell

Abstract

Background: Sodium taurocholate co-transportering polypeptide (NTCP, SLC10A1) is a vital bile acid transporter and the functional receptor of hepatitis B and D virus. The oligomerization of NTCP is important for the structural study of its interaction with HBV preS1 peptide.

Methods: Recombinant NTCPs were expressed in Sf9 host cell using baculoviruses. Function of recombinant NTCP was verified by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method. A quantitative fluorescence resonance energy transfer (FRET) method was established to analyze the interaction between NTCP wild type (WT) and mutants. Co-immunoprecipitation (Co-IP) was used to test the interaction between NTCP variants.

Results: Sub-cellular location of recombinant NTCPs varies with the modification of NTCP. Bands of monomer, dimer and oligomers were shown in gel analysis of NTCP. Significant FRET was observed between cyan florescence protein (CFP) tagged NTCP and yellow florescence protein (YFP) tagged NTCP. FRET efficiency between CFP- and YFP-NTCP S267F mutants was lower than WT. Co-IP results showed that S267F interacts with WT NTCP when co-expressed in cell.

Conclusion: Dimer is the predominant form of NTCP expressed in Sf9 when solubilized with detergent. FRET and Co-IP analysis support that NTCP forms oligomers in Sf9 cell.

General significance: Our results showed that NTCP formed oligomers in Sf9 cell. Meanwhile the FRET analysis of NTCP variants further elucidated the molecular mechanism of NTCP oligomerization.

Keywords: Dimer; FRET; NTCP; Oligomerization.