Structural and functional insights into δ-poly-L-ornithine polymer biosynthesis from Acinetobacter baumannii

Area of Science:

• Microbiology
• Biochemistry
• Natural Products Chemistry

Background:

• Cationic homo-polyamino acid (CHPA) peptides with isopeptide bonds are known from Actinomycetes.
• No CHPA production has been previously reported from other bacterial species.

Purpose of the Study:

• To identify and characterize novel CHPA synthetases and their products from bacteria beyond Actinomycetes.
• To investigate the enzymatic activity and substrate specificity of a newly identified enzyme from Acinetobacter baumannii.
• To explore the biological activity and potential applications of the synthesized CHPA.

Main Methods:

• Enzymatic assays using purified adenylation domain of PosA.
• Structural analysis of the adenylation domain.
• Biochemical characterization of the enzymatic product, poly-L-ornithine.
• Chemical synthesis and biological activity testing of poly-L-ornithine.
• Genome mining for homologous enzymes.

Main Results:

• A novel δ-poly-L-ornithine synthetase (PosA) was identified in Acinetobacter baumannii.
• PosA utilizes L-ornithine to produce poly-L-ornithine with 7-12 amino acid units and isopeptide linkages.
• Chemically synthesized poly-L-ornithine exhibits antifungal activity.
• Structural and biochemical analyses identified key substrate binding residues in PosA.
• Homologous enzymes with different substrate specificities were identified in other bacteria.

Conclusions:

• Acinetobacter baumannii produces poly-L-ornithine via the novel enzyme PosA.
• Poly-L-ornithine represents a new class of CHPA with potential antifungal applications.
• The study expands the known microbial diversity of CHPA production and suggests further exploration of uncharacterized natural products.