A Potent Host Defense Peptide Triggers DNA Damage and Is Active against Multidrug-Resistant Gram-Negative Pathogens

Area of Science:

• Microbiology
• Biochemistry
• Medicinal Chemistry

Background:

• Gram-negative bacteria pose significant public health threats due to widespread antibiotic resistance.
• Their complex cell structure necessitates novel antimicrobial strategies.
• Tunicate host defense peptide (HDP) Clavanin A shows promise against these pathogens, especially with zinc.

Purpose of the Study:

• To elucidate the novel mechanism by which Clavanin A, potentiated by Zn(II), inhibits Gram-negative bacteria.
• To confirm DNA damage as a key effect of Clavanin A treatment.
• To investigate the role of Zn(II) in Clavanin A's antimicrobial activity.

Main Methods:

• Utilized *E. coli* TD172 (Δ*recA::kan*) and TUNEL assay for *in cellulae* DNA damage detection.
• Performed *in vitro* assays to determine the requirement of Zn(II) for nuclease activity.
• Employed QM/MM calculations to model the DNA cleavage mechanism.
• Applied bacterial cytological profiling (BCP), CD spectroscopy, and SPR with EIS to reconcile findings with prior studies.

Main Results:

• Clavanin A treatment induces DNA damage in *E. coli*.
• Zn(II) ions are essential for the observed nuclease activity of Clavanin A.
• QM/MM calculations revealed Zn(II) activates DNA cleavage by facilitating nucleophilic attack from water.
• Integrated biophysical and microbiological techniques confirmed the DNA-damaging mechanism.

Conclusions:

• Clavanin A exhibits a novel DNA-damaging mechanism of action, dependent on Zn(II) for its nuclease activity.
• This mechanism provides a new avenue for developing therapeutics against antibiotic-resistant Gram-negative bacteria.
• The findings may facilitate the discovery of similar host defense peptides for antimicrobial drug development.