Lysobactin also known as katanosin B is a potent antibiotic with in vivo efficacy against and (MRSA) and multidrug-resistant streptococcal infections but clinical failure due to Tigecycline vancomycin resistance is increasingly common. attention not only because it represents a new structural class but also because it was shown to bind cell wall precursors from multiple biosynthetic pathways.5 In the course of our efforts to identify potent antimicrobial natural products from novel and known producing organisms we found extracts of is composed of thick layers of PG further modified with covalently bound WTA.7 The PG layers are essential for survival because they Tigecycline stabilize the cell membrane against high turgor pressure thereby preventing osmotic lysis. As shown in Figure 2 the PG precursor Lipid II (LipidIIGly5) is synthesized inside the cell on an undecaprenyl phosphate (Und-P) “carrier lipid” and then flipped outside where it is polymerized and cross-linked to make mature PG.8 Polymerization releases undecaprenyl pyrophosphate (Und-PP) which is dephosphorylated and recycled into the cell so that more Lipid II can be produced.9 The WTA biosynthetic pathway also involves intracellular assembly of a precursor on the Und-P carrier.7 After translocation to the surface of the cell this precursor is attached to the C6 hydroxyl of residues in PG through a phosphodiester bond liberating the carrier lipid.7 Vancomycin inhibits PG biosynthesis by binding to a d-Ala-d-Ala found at the terminus of the stem Tigecycline peptide of Lipid II while ramoplanin and teixobactin bind to a region of Lipid II that includes the pyrophosphate and the first sugar but not the stem peptide.2b 4 5 Teixobactin was also reported to bind a lipid-linked WTA precursor; therefore it was proposed that teixobactin kills by inhibiting both the PG and WTA biosynthetic pathways.5 Figure 2 Schematic of pathways for biosynthesis of lipid-linked PG and WTA precursors from the common intermediate Und-P. Compounds targeting PG and WTA biosynthesis are shown in purple and blue respectively. Lysobactin also known as katanosin B is produced by several genera of Gram-negative gliding bacteria found in soil. First reported in 1987 it was shown to inhibit PG biosynthesis and found to have outstanding in vitro activity against MRSA and vancomycin-resistant (VRE) as well as efficacy against systemic staphylococcal and streptococcal infections in mice.10 Although Tigecycline it was speculated to act as a substrate binder experimental evidence to establish this mechanism of action has not been reported.2 In 2007 Tigecycline two groups independently described the total synthesis of lysobactin and in 2011 the gene cluster was identified and characterized.11 To enable assessment of analogues for possible development we further characterized lysobactin’s activity and determined its mechanism of action. We found that lysobactin is rapidly bactericidal against and also has significant activity against mycobacteria (Figures 3 and S2). The colony forming units (CFUs) of a growing culture treated with lysobactin at 1.5 treated with no antibiotic (black circles) vancomycin (blue triangles) or lysobactin (red squares) at 2× … To determine whether lysobactin could be a substrate binder we added exogenous cell wall precursors to treated with lysobactin. Whereas the stem peptide mimic Lys-d-Ala-d-Ala antagonized the effects of vancomycin it had no effect on the MIC of lysobactin as previously reported.13 In contrast synthetic Lipid I14 and an analogue lacking the stem peptide protected from killing by lysobactin. These results suggested that lysobactin does indeed act via a substrate-binding mechanism (Figure 3c and S3). To confirm a substrate-binding mechanism Tigecycline and characterize lysobactin’s recognition preferences we monitored the reaction rate as a Rabbit polyclonal to AMID. function of substrate concentration for three enzymes that use cell wall precursors MurG SgtB and TagB. MurG catalyzes the formation of Lipid II from Lipid I; SgtB catalyzes the polymerization of the PG precursor Lipid II; TagB catalyzes the transfer of phosphoglycerol to a lipid-linked WTA disaccharide intermediate (Figure 2).14–16 Substrate binders produce a characteristic enzyme inhibition curve in which the reaction rate is negligible at low substrate concentrations because there is no free substrate but jumps as soon as substrate becomes.