Design of a Human Defensin 5-Derived Linear Peptide with Potent Antibacterial Efficacy Against Carbapenem-Resistant Acinetobacter baumannii

The increasing incidence of infections caused by carbapenem-resistant Acinetobacter baumannii (CRAB) poses a serious threat to global public health, yet treatment options remain scarce. Human defensins (HDs) represent a promising alternative to conventional antibiotics for combating superbugs; however, their structural complexity often hinders synthetic accessibility. Here, we report the rational design of HD5lp5, a linear peptide derived from HD5 through the removal of disulfide bonds and the introduction of arginine residues. This derivative exhibits potent bactericidal activity against CRAB and retains bioactivity in complex physiological environments. Mechanistically, HD5lp5 binds to bacterial lipid A with a dissociation constant of 1.81 nM and destroys membrane integrity in a dose-dependent manner, inducing the leakage of intracellular contents. Beyond membrane disruption, its structural flexibility enables translocation into bacteria. In vitro translation assay reveals that HD5lp5 inhibits ribosomal translation with a half-maximal inhibitory concentration of 0.38 μM. Notably, HD5lp5 exhibits no apparent toxicity in vivo, and it effectively eliminates CRAB colonisation in murine models of intra-abdominal sepsis and irradiation-assisted pulmonary infection, thereby increasing survival rates. Our findings establish HD5lp5 as a promising preclinical candidate for treating life-threatening CRAB.