Target Prioritization

Although proteins are conserved in relevant pathogens and are essential for bacterial growth, they might not be equally suitable as antibacterial targets. For instance, significant dissimilarity of targets to homologous human proteins or, even better, nonexistence of homologues in humans diminishes the danger of target-based toxicity of specific inhibitors in the host. Such a bacterial selectivity criterion, which can easily be evaluated with bioinformatics tools, is not enough by a long way for prioritization of proteins according to their suitability as targets. Considerable experimental effort is necessary to clarify target-related physiological aspects. Conditional mutants represent valuable tools with which to address the relevant questions. Firstly, they are instrumental in measuring the degree of target downregulation required for reaching bacteriostatic or bacteriolytic effects. However, no systematic study has been performed to date. Secondly, conditional mutants might aid in clarifying whether by-pass mutations can readily suppress the defect in an essential gene, which makes this target less interesting for drug screening. For instance, in some organisms such as S. aureus the essential role of the peptide deformyase PDF is suppressed by mutation of the formyltransferase Fmt, which makes peptide deformylation superfluous [62]. In other organisms such as S. pneumoniae the Fmt proved to be essential, impairing a suppressor mutation in Fmt [63]. However, cross-species genome-wide target prioritization is still in its infancy, since for many targets information about the cellular consequences of inhibiting their function in different species is insufficient, not to mention that some targets themselves are not yet functionally characterized. The number of under-explored targets increases especially when focusing on functions conserved in narrowed spectra of bacteria. Growth studies with various supplements, cytological evaluation, metabolic labeling experiments, and transcriptome and proteome analyses with conditional mutants under semipermissive conditions might aid in the functional characterization of the respective genes.

0 0

Post a comment