Unravelling the Antimicrobial Action Mechanism of Ribosomal Protein S30

Ribosomal protein S30 (RS30) exhibits potent antimicrobial activity against a broad spectrum of bacteria. Despite its efficacy, the underlying action mechanism remained elusive. In this study, we unravel the fundamental mechanism by which RS30 exerts its bactericidal effects, using a combination of microbiological assays and advanced biophysical techniques. Microbiological analyses reveal that RS30 kills bacteria primarily through membrane depolarization, despite limited membrane permeabilization, indicating an unconventional mode of action involving no or partial lysis of the membrane. Importantly, RS30 demonstrates time-dependent bactericidal activity with no detectable cytotoxicity toward mammalian cells, underscoring its high selectivity. This selective action was further confirmed using biophysical experiments on model membrane systems composed of anionic (bacterial mimic) and zwitterionic (mammalian mimic) phospholipids. Our measurements suggested that RS30 preferentially binds to anionic membranes via electrostatic interactions, undergoes a conformational transition from a random coil to an {\alpha}-helix upon binding, and induces vesicle aggregation. Quasielastic neutron scattering (QENS) measurements provide microscopic insights, showing that RS30 significantly restricts the lateral diffusion of anionic lipids, thereby perturbing membrane dynamics and increasing susceptibility to external stress. Together, our findings uncover important insights into the antimicrobial action mechanism of RS30, characterized by selective membrane interaction, structural transformation, and dynamic modulation of lipid membranes.