Single Deletion Unmasks Hidden Anti-Gram-Negative Bacterial Activity of an Insect Defensin-Derived Peptide

Insect
defensins are a large family of antimicrobial peptides primarily
active against Gram-positive bacteria. Here, we explore their hidden
anti-Gram-negative bacterial potential via a nature-guided strategy
inspired by natural deletion variants of Drosophila defensins. Referring to these variants, we deleted the equivalent
region of an insect defensin with the first cysteine-containing N-terminus,
and the last three cysteine-containing C-terminal regions remained.
This 15-mer peptide exhibits low solubility and specifically targets
Gram-positive bacteria. Further deletion of alanine-9 remarkably improves
its solubility, unmasks its hidden anti-Gram-negative bacterial activity,
and alters its states in different environments. Intriguingly, compared
with the oxidized form, the 14-mer reduced peptide shows increased
activity on Gram-positive and Gram-negative bacteria through a membrane-disruptive
mechanism. The broad-spectrum activity and tolerance to high-salt
environments and human serum, together with no toxicity to mammalian
or human cells, make it a promising candidate for the design of new
peptide antibiotics against Gram-negative bacterial infections.