Exploring the interaction mechanism between the programmed death-ligand 1 protein and scutellarin via multi-spectroscopy and computer simulation

The programmed death-ligand 1 (PD-L1) protein plays a key role in immune responses. Scutellarin (SCU), as a flavonoid, has a variety of bioactivities. In this study, the human PD-L1 was obtained by expression and purification, and the interaction mechanisms between PD-L1 and SCU were revealed through multi-spectroscopy and computer simulation. Fluorescence data indicated that the quenching of PD-L1 by SCU was mainly static quenching, and primarily driven by hydrogen bonding and van der Waals forces. The binding constant (K_a) was decreased from 2.05 ± 0.55 × 10⁴ L·mol^-1 to 0.28 ± 0.08 × 10⁴ L·mol^-1 with increasing temperature. Meanwhile, the changes in the microenvironment of PD-L1 were revealed by the synchronous and the 3D fluorescence data. In addition, the melting temperature of PD-L1 increased by 1.67 °C after binding with SCU. Moreover, the circular dichroism data showed that SCU changed the secondary structure of PD-L1 by increasing α-helix content and decreasing β-sheet content. Furthermore, the binding modes between SCU and PD-L1 and the key residues involved in the interaction were revealed by molecular docking and molecular dynamics. These findings supported SCU as an alternative ICB therapeutic strategy and provided evidence for computer-based drug design strategies.