This research paper characterizes six new karnamycins (E₁-E₆) isolated from the *Lechevalieria rhizosphaerae* NEAU-A2 actinobacterium. The study elucidates the biosynthesis of the fully substituted hydroxypyridine moiety through a hybrid polyketide synthase-nonribosomal peptide synthetase (PKS-NRPS), two flavoprotein monooxygenases (FPMOs), and a methyltransferase. The researchers utilized isotopic labeling, genome mining, and enzymatic characterization to propose the biosynthetic pathway. Structural analysis using AlphaFold protein structure predictions, molecular docking, and site-directed mutagenesis revealed unique active site residues in the pyridine hydroxylases. Importantly, karnamycins exhibit significant angiotensin-converting enzyme (ACE) inhibitory activity, suggesting their potential as therapeutic agents for hypertension and related cardiovascular diseases.
