ИСТИНА

Klebsazolicin (KLB) is a novel Klebsiella pneumonia peptide antibiotic targeting the exit tunnel of bacterial ribosome. KLB contains an N-terminal amidine ring and four azoles. These modifications are required for activity and are introduced into a ribosomally-synthesized precursor by the KlpBCD maturation enzyme complex. We reconstituted a highly efficient in vitro system for KLB production and showed that the KlpD subunit is responsible for both the azole and amidine formation. We further show that the amidine ring is formed concomitantly with proteolytic cleavage of azole-containing pro-KLB by a specialized TldD/E protease. KlpD belongs to the YcaO-domain protein family. Members of the family are diverse enzymes known to activate peptide carbonyls during natural product biosynthesis leading to the formation of azoline, macroamidine, and thioamide groups. The ability of KlpD to simultaneously perform two distinct types of modifications is unprecedented for known YcaO proteins. The versatility of KlpD opens up possibilities for rational introduction of modifications into various peptide backbones.