NMR characterization of the interaction between Bcl-xL and the BH3-like motif of hepatitis B virus X protein

Hepatitis B virus X protein (HBx) possesses a BH3-like motif that directly interacts with the antiapoptotic proteins, Bcl-2 and Bcl-x(L). Here we report the interaction between the HBx BH3-like motif and Bcl-x(L), as revealed by nuclear magnetic resonance spectroscopy. Our results showed that this motif binds to the common BH3-binding hydrophobic groove on the surface of Bcl-x(L), with a binding affinity of 89 mu M. Furthermore, we examined the role of the tryptophan residue (Trp120) in this motif in Bcl-x(L), binding using three mutants. The W120A mutant showed weaker binding affinity (294 mu M) to Bcl-x(L), whereas the W120L and W120F mutants exhibited almost equivalent binding affinity to the wild-type. These results indicate that the bulky hydrophobic residues are important for Bcl-x(L), binding. The findings will be helpful in understanding the apoptosis networks between viral proteins and host factors. (C) 2019 Elsevier Inc. All rights reserved.