Influence of Lipophilicity on the Antibacterial Activity of Polymyxin Derivatives and on Their Ability to Act as Potentiators of Rifampicin.

Novel polymyxin derivatives are often classified either as having direct activity against Gram-negative pathogens or as compounds inactive in their own right, which through permeabilization of the outer membrane act as potentiators of other antibiotics. Here, we report the systematic investigation of the influence of lipophilicity on microbiological activity (including against strains with reduced susceptibility to polymyxins), potentiation of rifampicin, and toxicity within a series of next-generation polymyxin nonapeptides. We demonstrate that the lipophilicity at the N-terminus and amino acids 6 and 7 in the cyclic peptide core is interchangeable and that the activity, ability to potentiate, and cytotoxicity all appear to be primarily driven by overall lipophilicity.

Design of Next Generation Polymyxins with Lower Toxicity: The Discovery of SPR206.

Polymyxins are an important class of antibiotics for the treatment of bacterial infections due to multidrug resistant Gram-negative pathogens. However, their clinical utility is limited by nephrotoxicity. Here, we report a series of promising next generation polymyxin nonapeptides identified on the basis of our understanding of the relationship of structure with activity, cytotoxicity, and kidney compartment accumulation.

Antibacterial activity of the novel semisynthetic lantibiotic NVB333 in vitro and in experimental infection models.

NVB333 is a novel semisynthetic lantibiotic derived from the amide coupling of 3,5-dichlorobenzylamine to the C-terminal of deoxyactagardine B. The in vitro activity of NVB333 includes efficacy against clinically relevant pathogens including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus spp. NVB333 shows no cross-resistance with other antibiotics tested and a very low propensity for resistance development.

Generation of an actagardine A variant library through saturation mutagenesis.

The lantibiotic actagardine A is nineteen amino acids in length and comprises three intertwined C-terminal methyllanthionine-bridged rings and an N-terminal lanthionine-bridged ring. Produced by the actinomycete Actinoplanes garbadinensis ATCC 31049, actagardine A demonstrates antibacterial activity against important Gram-positive pathogens. This activity combined with its ribosomal synthesis makes it an attractive target for the generation of lantibiotic variants with improved biological activity.

Organization of the biosynthetic genes encoding deoxyactagardine B (DAB), a new lantibiotic produced by Actinoplanes liguriae NCIMB41362.

Deoxyactagardine B (DAB) is a hitherto unknown type B lantibiotic, produced by Actinoplanes liguriae NCIMB41362. The mature peptide is 19 amino acids in length and structurally analogous to actagardine, differing by two amino acids (V15L and I16V) and the absence of a sulfoxide bond between residues 14 and 19. The biosynthetic genes encoding DAB are clustered, and in addition to the structural gene ligA include genes believed to encode for the proteins responsible for the modification, transport and regulation of DAB synthesis.

Biosynthesis of the putative siderophore erythrochelin requires unprecedented crosstalk between separate nonribosomal peptide gene clusters.

The genome of the erythromycin-producing bacterium Saccharopolyspora erythraea contains many orphan secondary metabolite gene clusters including two (nrps3 and nrps5) predicted to govern biosynthesis of nonribosomal peptide-based siderophores. We report here the production by S. erythraea, even under iron-sufficient conditions, of a 2,5-diketopiperazine siderophore candidate we have named erythrochelin.

Dissecting structural and functional diversity of the lantibiotic mersacidin.

Mersacidin is a tetracyclic lantibiotic with antibacterial activity against Gram-positive pathogens. To probe the specificity of the biosynthetic pathway of mersacidin and obtain analogs with improved antibacterial activity, an efficient system for generating variants of this lantibiotic was developed. A saturation mutagenesis library of the residues of mersacidin not involved in cycle formation was constructed and used to validate this system.

Organization of the genes encoding the biosynthesis of actagardine and engineering of a variant generation system.

The biosynthetic pathway of the type B lantibiotic actagardine (formerly gardimycin), produced by Actinoplanes garbadinensis ATCC31049, has been cloned, sequenced and annotated. The gene cluster contains the gene garA that encodes the actagardine prepropeptide, a modification gene garM, involved in the dehydration and cyclization of the prepeptide, several putative transporter and regulatory genes as well as a novel luciferase-like monooxygenase gene designated garO. Expression of these genes in Streptomyces lividans resulted in the production of ala(0)-actagardine while deletion of the garA gene from A.

A new modular polyketide synthase in the erythromycin producer Saccharopolyspora erythraea.

A previously unidentified set of genes encoding a modular polyketide synthase (PKS) has been sequenced in Saccharopolyspora erythraea, producer of the antibiotic erythromycin. This new PKS gene cluster (pke) contains four adjacent large open reading frames (ORFs) encoding eight extension modules, flanked by a number of other ORFs which can be plausibly assigned roles in polyketide biosynthesis. Disruption of the pke PKS genes gave S.