Purification, crystallization and preliminary X-ray crystallographic studies of the Mycobacterium tuberculosis DNA gyrase ATPase domain.

Mycobacterium tuberculosis DNA gyrase, a nanomachine involved in the regulation of DNA topology, is the only type II topoisomerase present in this organism and hence is the sole target of fluoroquinolones in the treatment of tuberculosis. The ATPase domain provides the energy required for catalysis by ATP hydrolysis. Two constructs corresponding to this 43 kDa domain, Mtb-GyrB47(C1) and Mtb-GyrB47(C2), have been overproduced, purified and crystallized. Diffraction data were collected from three crystal forms. The crystals belonged to space groups P1 and P21 and diffracted to resolutions of 2.9 and 3.3 Å, respectively.

Bacterial production of biologically active canine interleukin-1beta by seamless SUMO tagging and removal.

Interleukin 1beta (IL-1beta) is a potent stimulator of extracellular matrix degradation in models of osteoarthritis (OA). In contrast to bovine explant models which effectively respond to recombinant human IL-1beta, canine models are relatively refractory to human IL-1beta stimulation. Canine IL-1beta cDNA was cloned in order to produce a fully potent species matched preparation of IL-1beta for use specifically in canine models of OA. Established methods for the production of various orthologous IL-1beta proteins from different species are problematic due to the exquisite sensitivity of the mature IL-1beta product to N-terminal variations and the intrinsic technical challenges associated with producing an unmodified product. We have applied a seamless method of SUMO tagging and removal in order to produce a homogeneous unmodified preparation of canine IL-1beta from Escherichia coli which was found to be a potent inducer of aggrecanase activity in isolated canine articular chondrocytes. This method combines highly efficient aspects of seamless plasmid engineering, protein purification, and precise tag removal.

Phylogeny of gamma-proteobacteria: resolution of one branch of the universal tree?

The reconstruction of bacterial evolutionary relationships has proven to be a daunting task because variable mutation rates and horizontal gene transfer (HGT) among species can cause grave incongruities between phylogenetic trees based on single genes. Recently, a highly robust phylogenetic tree was constructed for 13 gamma-proteobacteria using the combined alignments of 205 conserved orthologous proteins.1 Only two proteins had incongruent tree topologies, which were attributed to HGT between Pseudomonas species and Vibrio cholerae or enterics. While the evolutionary relationships among these species appears to be resolved, further analysis suggests that HGT events with other bacterial partners likely occurred; this alters the implicit assumption of gamma-proteobacteria monophyly. Thus, any thorough reconstruction of bacterial evolution must not only choose a suitable set of molecular markers but also strive to reduce potential bias in the selection of species.

A global approach to identify novel broad-spectrum antibacterial targets among proteins of unknown function.

Attempted allelic replacement of 144 Streptococcus pneumoniae open reading frames of previously uncharacterized function led to the identification of 36 genes essential for growth under laboratory conditions. Of these, 14 genes (obg, spoIIIJ2, trmU, yacA, yacM, ydiC, ydiE, yjbN, yneS, yphC, ysxC, ytaG, yloI and yxeH4) were also essential in Staphylococcus aureus and Haemophilus influenzae or Escherichia coli, 2 genes (yrrK and ydiB) were only essential in H. influenzae as well as S. pneumoniae and 8 genes were necessary for growth of S.pneumoniae and S. aureus and did not have a homolog in H. influenzae(murD2, ykqC, ylqF, yqeH, ytgP, yybQ) or were not essential in that organism (yqeL, yhcT). The proteins encoded by these genes could represent good targets for novel antibiotics covering different therapeutic profiles. The putative functions of some of these essential proteins, inferred by bioinformatic analysis, are presented. Four mutants, with deletions of loci not essential for in vitro growth, were found to be severely attenuated in a murine respiratory tract infection model, suggesting that not all targets for antibacterial therapeutics are revealed by simple in vitro essentiality testing. The results of our experiments together with those collated from previously reported studies including Bacillus subtilis, E. coli and Mycoplasma sp. demonstrate that gene conservation amongst bacteria does not necessarily indicate that essentiality in one organism can be extrapolated to others. Moreover, this study demonstrates that different experimental procedures can produce apparently contradictory results.

Bioinformatics and the discovery of novel anti-microbial targets.

Genomic research is playing a critical role in the discovery of new anti-microbial drugs. The rapid increase in bacterial and eukaryotic genome sequences allows for new and innovative ways for obtaining antimicrobial protein targets. Here, we describe a two level strategy for target identification and validation using computers (in silico). First, large scale comparative analyses of genome sequences were used to identify highly conserved genes which might be essential for in vitro and/or in vivo survival of bacterial pathogens. Lab-based experiments provided confirmation or validation of the hypothesis of in silico essentiality for over 350 individual genes. Over 200 validated, broad spectrum; yet highly specific gene targets, were identified in community infection pathogens. The second part of the target discovery strategy is an in-depth evolutionary, structural and cellular analysis of key drug targets. As an example, phylogenetic and structural analyses suggest that sequence and binding-pocket conservation in FabH (beta-ketoacyl-ACP synthase III) would allow for the development of small molecule inhibitors not only effective against a broad species spectrum of community bacterial pathogens but also as potential new therapies for tuberculosis and malaria.