研究発表

KcsA is a pH-dependent K+ channel, which opens under acidic conditions. Under the acidic conditions, KcsA switches between open and closed states on a millisecond timescale (msec-gating), which regulates the K+ permeation in cells. However, the structural mechanism of the msec-gating has remained unclear. In this research, we designed KcsA mutants with different open probabilities in the msec-gating, and conducted NMR experiments on these mutants. We revealed that KcsA undergoes an equilibrium between two conformations, which differ in structures of a cytoplasmic transmembrane gate, and the ratios of these conformations well correlate with the open probabilities in the msec-gating. From these results, we conclude that the conformational equilibrium in the cytoplasmic transmembrane gate leads to the msec-gating.

The development of safe and potent inhibitors of hepatitis B virus (HBV) entry is crucial to prevent new infections and achieve complete virus elimination in HBV carriers. Persistent HBV carriers have partial hepatocyte infection. If entry into uninfected hepatocytes could be completely inhibited, the number of infected cells would decrease over time. We previously reported that INT-767, a bile acid derivative, inhibits HBV entry by acting directly on the preS1 region. Due to safety concerns with INT-767, we aimed to develop a safer anti-HBV agent based on its mechanism of action. Methods: A bile acid derivative library, based on the structure of INT-767, was created. We performed a preS1 binding assay to quantitatively evaluate the inhibitory effect of binding between the preS1 region and Sodium-taurocholate co-transporting polypeptide (NTCP) in library compounds. A three-dimensional quantitative structure-activity relationship (3D-QSAR) model was developed to predict anti-HBV activity from the structures of new candidate compounds. Results: Analysis of the preS1 binding assay results revealed important structures for anti-HBV activity. Bile acid derivatives inhibiting preS1 and NTCP binding shared a common structure, including INT-767. Constructing a 3D-QSAR model using all assay data enabled more detailed predictions of anti-HBV efficacy. Further studies on various bile acid derivatives revealed novel structural features that enhance anti-HBV efficacy. Synthesizing newly designed lead compounds with these features and conducting in vitro HBV infection models demonstrated anti-HBV effects that exceeded those of existing lead compounds. Conclusion: The 3D-QSAR model, constructed from data on the anti-HBV effects of bile acid derivatives, led to the development of novel bile acid derivatives with more potent anti-HBV activity. Future work with these derivatives will collect data on anti-HBV effects and cytotoxicity, enhancing predictive accuracy for further development.