Brief communication: Mass spectroscopic characterization of tetracycline in the skeletal remains of an ancient population from Sudanese Nubia 350-550 CE

Histological evidence of tetracycline use has been reported in an ancient X-Group population (350-550 CE) from Sudanese Nubia (Bassett et al., 1980). When bone samples were examined by fluorescent microscopy under UV light at 490 A yellow-green fluorophore deposition bands, similar to those produced by tetracycline, were observed, suggesting significant exposure of the population to the antibiotic. These reports were met skeptically with claims that the fluorescence was the result of postmortem taphonomic infiltration of bacteria and fungi. Herein, we report the acid extraction and mass spectroscopic characterization of the antibiotic tetracycline from these samples. The bone samples were demineralized in anhydrous hydrogen fluoride which dissolved the bone-complexed tetracycline, followed by isolation by solid phase extraction on reverse-phase media. Chemical characterization by high pressure liquid chromatography mass-spectroscopic procedures showed that the retention times and mass spectra of the bone extract were identical to tetracycline when treated similarly. These results indicate that a natural product tetracycline was detectable within the sampled bone and was converted to the acid-stable form, anhydrotetracycline, with a mass + H of 427.1 amu. Our findings show that the bone sampled is labeled by the antibiotic tetracycline, and that the NAX population ingested and were exposed to tetracycline-containing materials in their dietary regime.

Discovery and syntheses of "superbug challengers"-platensimycin and platencin

Bacteria have developed resistance to almost all existing antibiotics known today and this has been a major issue over the last few decades. The search for a new class of antibiotics with a new mode of action to fight these multiply-drug-resistant strains, or "superbugs", allowed a team of scientists at Merck to discover two novel antibiotics, platensimycin and platencin using advanced screening strategies, as inhibitors of bacterial fatty acid biosynthesis, which is essential for the survival of bacteria. Though both these antibiotics are structurally related, they work by slightly different mechanisms and target different enzymes conserved in the bacterial fatty acid biosynthesis. This Focus Review summarizes the synthetic and biological aspects of these natural products and their analogues and congeners.

Recent advances in the chemistry and biology of naturally occurring antibiotics

Ever since the world-shaping discovery of penicillin, nature's molecular diversity has been extensively screened for new medications and lead compounds in drug discovery. The search for agents intended to combat infectious diseases has been of particular interest and has enjoyed a high degree of success. Indeed, the history of antibiotics is marked with impressive discoveries and drug-development stories, the overwhelming majority of which have their origin in natural products. Chemistry, and in particular chemical synthesis, has played a major role in bringing naturally occurring antibiotics and their derivatives to the clinic, and no doubt these disciplines will continue to be key enabling technologies. In this review article, we highlight a number of recent discoveries and advances in the chemistry, biology, and medicine of naturally occurring antibiotics, with particular emphasis on total synthesis, analogue design, and biological evaluation of molecules with novel mechanisms of action.

Biosynthesis of cervimycin C, an aromatic polyketide antibiotic bearing an unusual dimethylmalonyl moiety

Cervimycin C is the major component of an antibiotic complex produced by Streptomyces tendae HKI-179 consisting of a tetracycline-type aglycon, six tridesoxysugars and a rare dimethylmalonyl moiety. The biosynthetic origin of cervimycin was studied by molecular studies and feeding experiments, which reveal that the dimethylmalonate unit is not derived from malonate, but from valine.

Solution structure and dynamics of oxytetracycline polyketide synthase acyl carrier protein from Streptomyces rimosus

Type II polyketide synthases (PKSs) utilize a dedicated and essential acyl carrier protein (ACP) in the biosynthesis of a specific polyketide product. As part of our ongoing studies into the mechanisms and control of polyketide biosynthesis, we report the second structure of a polyketide synthase ACP. In this work, multidimensional, heteronuclear NMR was employed to investigate the structure and dynamics of the ACP involved in the biosynthesis of the commonly prescribed polyketide antibiotic, oxytetracycline (otc). An ensemble of 28 structures of the 95 amino acid otc ACP (9916Da) was computed by simulated annealing with the inclusion of 1132 experimental restraints. Atomic RMSDs about the mean structure for all 28 models is 0.66 A for backbone atoms, 1.15 A for all heavy atoms (both values calculated for the folded part of the protein (residues 3-80)), and 0.41 A for backbone atoms within secondary structure. Otc ACP adopts the typical right-handed, four-helix fold of currently known ACPs but with the addition of a 13-residue flexible C-terminus. A comparison of the global folds of all structurally characterized ACPs is described, illustrating that PKS ACPs show clear differences as well as similarities to FAS ACPs. (15)N relaxation experiments for the protein backbone also reveal that the long loop between helices I and II is flexible and helix II, a proposed site of protein-protein interactions, shows conformational exchange. The helices of the ACP form a rigid scaffold for the protein, but these are interspersed with an unusual proportion of flexible linker regions.

Phosphate control of oxytetracycline production by Streptomyces rimosus is at the level of transcription from promoters overlapped by tandem repeats similar to those of the DNA-binding sites of the OmpR family

Physiological studies have shown that Streptomyces rimosus produces the polyketide antibiotic oxytetracycline abundantly when its mycelial growth is limited by phosphate starvation. We show here that transcripts originating from the promoter for one of the biosynthetic genes, otcC (encoding anhydrotetracycline oxygenase), and from a promoter for the divergent otcX genes peak in abundance at the onset of antibiotic production induced by phosphate starvation, indicating that the synthesis of oxytetracycline is controlled, at least in part, at the level of transcription. Furthermore, analysis of the sequences of the promoters for otcC, otcX, and the polyketide synthase (otcY) genes revealed tandem repeats having significant similarity to the DNA-binding sites of ActII-Orf4 and DnrI, which are Streptomyces antibiotic regulatory proteins (SARPs) related to the OmpR family of transcription activators. Together, the above results suggest that oxytetracycline production by S. rimosus requires a SARP-like transcription factor that is either produced or activated or both under conditions of low phosphate concentrations. We also provide evidence consistent with the otrA resistance gene being cotranscribed with otcC as part of a polycistronic message, suggesting a simple mechanism of coordinate regulation which ensures that resistance to the antibiotic increases in proportion to production.

The Streptomyces peucetius dpsY and dnrX genes govern early and late steps of daunorubicin and doxorubicin biosynthesis

The Streptomyces peucetius dpsY and dnrX genes govern early and late steps in the biosynthesis of the clinically valuable antitumor drugs daunorubicin (DNR) and doxorubicin (DXR). Although their deduced products resemble those of genes thought to be involved in antibiotic production in several other bacteria, this information could not be used to identify the functions of dpsY and dnrX. Replacement of dpsY with a mutant form disrupted by insertion of the aphII neomycin-kanamycin resistance gene resulted in the accumulation of UWM5, the C-19 ethyl homolog of SEK43, a known shunt product of iterative polyketide synthases involved in the biosynthesis of aromatic polyketides. Hence, DpsY must act along with the other components of the DNR-DXR polyketide synthase to form 12-deoxyaklanonic acid, the earliest known intermediate of the DXR pathway. Mutation of dnrX in the same way resulted in a threefold increase in DXR production and the disappearance of two acid-sensitive, unknown compounds from culture extracts. These results suggest that dnrX, analogous to the role of the S. peucetius dnrH gene (C. Scotti and C. R. Hutchinson, J. Bacteriol. 178:73167321, 1996), may be involved in the metabolism of DNR and/or DXR to acid-sensitive compounds, possibly related to the baumycins found in many DNR-producing bacteria.