Myxobacterium-Produced Antibiotic TA (Myxovirescin) Inhibits Type II Signal Peptidase

Abstract

ABSTRACTAntibiotic TA is a macrocyclic secondary metabolite produced by myxobacteria that has broad-spectrum bactericidal activity. The structure of TA is unique, and its molecular target is unknown. Here, we sought to elucidate TA's mode of action (MOA) through two parallel genetic approaches. First, chromosomalEscherichia coliTA-resistant mutants were isolated. One mutant that showed specific resistance toward TA was mapped and resulted from an IS4insertion in thelppgene, which encodes an abundant outer membrane (Braun's) lipoprotein. In a second approach, the comprehensiveE. coliASKA plasmid library was screened for overexpressing clones that conferred TAr. This effort resulted in the isolation of thelspAgene, which encodes the type II signal peptidase that cleaves signal sequences from prolipoproteins. In whole cells, TA was shown to inhibit Lpp prolipoprotein processing, similar to the known LspA inhibitor globomycin. Based on genetic evidence and prior globomycin studies, a block in Lpp expression or prevention of Lpp covalent cell wall attachment confers TArby alleviating a toxic buildup of mislocalized pro-Lpp. Taken together, these data argue that LspA is the molecular target of TA. Strikingly, the gianttabiosynthetic gene cluster encodes twolspAparalogs that we hypothesize play a role in producer strain resistance.