Self Resistance to the Atypical Cationic Antimicrobial Peptide Edeine of Brevibacillus brevis Vm4 by the N-Acetyltransferase EdeQ

Edeines are atypical cationic peptides produced by Brevibacillus brevis Vm4 with broad-spectrum antimicrobial activity. These linear nonribosomal peptides bind to the 30S ribosomal subunit and block t-RNA binding to the P-site. To identify the mechanism of high-level self-resistance in the producing organism, the B. brevis Vm4 genome was sequenced and the edeine biosynthetic cluster discovered. A potential edeine-modifying enzyme, EdeQ, showed similarity to spermidine N-acetyltransferases. EdeQ was purified and shown to convert edeine to N-acetyledeine, which is inactive against cells in vivo and against cell-free extracts. Unexpectedly, tandem mass spectroscopy and nuclear magnetic resonance demonstrate that N-acylation occurs on the free amine of the internal diaminopropionic acid rather than the N-terminal spermidine polyamine. Acetylation of edeine by EdeQ abolishes its ability to inhibit translation, thus conferring resistance to the antibiotic in the producing organism.