The worldwide spread of antibiotic resistance in pathogenic bacteria raises serious concerns that today's front-line antibiotics may become ineffective. So the discovery of a new class of compound with enormous potential as antibiotics is of great interest. Platensimycin is the first member of a novel class of natural products that selectively kills bacteria by inhibiting FabF/FabB proteins, a mechanism of action that is not used by any agents in clinical use. It is a potent antibiotic with broad-spectrum activity against Gram-positive bacteria, including clinically relevant drug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus. The future of platensimycins is considered in the News pages, and see the antimicrobials Web Focus on http://tinyurl.com/g8omx. A new class of antibiotics that targets bacterial lipid biosynthesis is isolated from Streptomyces platensis, and demonstrates potent in vitro and in vivo activity against Gram-positive bacteria — including methicillin-resistant Staphylococcus species. Bacterial infection remains a serious threat to human lives because of emerging resistance to existing antibiotics. Although the scientific community has avidly pursued the discovery of new antibiotics that interact with new targets, these efforts have met with limited success since the early 1960s1,2. Here we report the discovery of platensimycin, a previously unknown class of antibiotics produced by Streptomyces platensis. Platensimycin demonstrates strong, broad-spectrum Gram-positive antibacterial activity by selectively inhibiting cellular lipid biosynthesis. We show that this anti-bacterial effect is exerted through the selective targeting of β-ketoacyl-(acyl-carrier-protein (ACP)) synthase I/II (FabF/B) in the synthetic pathway of fatty acids. Direct binding assays show that platensimycin interacts specifically with the acyl-enzyme intermediate of the target protein, and X-ray crystallographic studies reveal that a specific conformational change that occurs on acylation must take place before the inhibitor can bind. Treatment with platensimycin eradicates Staphylococcus aureus infection in mice. Because of its unique mode of action, platensimycin shows no cross-resistance to other key antibiotic-resistant strains tested, including methicillin-resistant S. aureus, vancomycin-intermediate S. aureus and vancomycin-resistant enterococci. Platensimycin is the most potent inhibitor reported for the FabF/B condensing enzymes, and is the only inhibitor of these targets that shows broad-spectrum activity, in vivo efficacy and no observed toxicity.

Platensimycin is a selective FabF inhibitor with potent antibiotic properties

Structural and functional organization of the animal fatty acid synthase.

Histone deacetylase is a metallo-enzyme with zinc at the active site. Compounds having a zinc-binding moiety, such as, for example, a hydroxamic acid group or a carboxylic acid group, can inhibit histone deacetylase. Histone deacetylase can repress gene expression, including expression of genes related to tumor suppression. Accordingly, inhibition of histone deacetylase can provide an alternate route for treating cancer, hematological disorders, e.g., hemoglobinopathies, and genetic related metabolic disorders, e.g., cystic fibrosis and adrenoleukodystrophy.

Histone deacetylase inhibitors

The type I fatty acid and polyketide synthases: a tale of two megasynthases.

The present invention relates to isolated polypeptides having cellulolytic enhancing activity and isolated polynucleotides encoding the polypeptides. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides.

Polypeptides having cellulolytic enhancing activity and polynucleotides encoding same

beta-Ketoacyl synthases involved in the biosynthesis of fatty acids and polyketides exhibit extensive sequence similarity and share a common reaction mechanism, in which the carbanion participating in the condensation reaction is generated by decarboxylation of a malonyl or methylmalonyl moiety; normally, the decarboxylation step does not take place readily unless an acyl moiety is positioned on the active-site cysteine residue in readiness for the ensuing condensation reaction. Replacement of the cysteine nucleophile (Cys-161) with glutamine, in the beta-ketoacyl synthase domain of the multifunctional animal fatty acid synthase, completely inhibits the condensation reaction but increases the uncoupled rate of malonyl decarboxylation by more than 2 orders of magnitude. On the other hand, replacement with Ser, Ala, Asn, Gly, and Thr compromises the condensation reaction without having any marked effect on the decarboxylation reaction. The affinity of the beta-ketoacyl synthase for malonyl moieties, in the absence of acetyl moieties, is significantly increased in the Cys161Gln mutant compared to that in the wild type and is similar to that exhibited by the wild-type beta-ketoacyl synthase in the presence of an acetyl primer. These results, together with modeling studies of the Cys --> Gln mutant from the crystal structure of the Escherichia coli beta-ketoacyl synthase II enzyme, suggest that the side chain carbonyl group of the Gln-161 can mimic the carbonyl of the acyl moiety in the acyl-enzyme intermediate so that the mutant adopts a conformation analogous to that of the acyl-enzyme intermediate. Catalysis of the decarboxylation of malonyl-CoA requires the dimeric form of the Cys161Gln fatty acid synthase and involves prior transfer of the malonyl moiety from the CoA ester to the acyl carrier protein domain and subsequent release of the acetyl product by transfer back to a CoA acceptor. These results suggest that the role of the Cys --> Gln beta-ketoacyl synthases found in the loading domains of some modular polyketide synthases likely is to act as malonyl, or methylmalonyl, decarboxylases that provide a source of primer for the chain extension reactions catalyzed by associated modules containing fully competent beta-ketoacyl synthases.

Ylva Lindqvist

Papers

Conversion of a beta-ketoacyl synthase to a malonyl decarboxylase by replacement of the active-site cysteine with glutamine.