New antibiotic discovery, novel screens, novel targets and impact of microbial genomics.

The clinical need for new classes of antibiotic continues to grow, as drug resistance erodes the efficacy of current therapies. Historically, most antibiotics were discovered by random screening campaigns, but over the past 20 years, this strategy has largely failed to deliver a sufficient range of chemical diversity to keep pace with changing clinical profiles. A more rational approach to drug hunting has been greatly potentiated by the availability of bacterial genomic information. The rapid progress in sequencing and analysis of these small, prokaryotic genomes has enabled the concomitant development of powerful new technologies that are already enhancing the potential utility of genomic information. The future promises versatile and precise tools to understand what makes a successful antibiotic and moreover the means to identify and evaluate novel classes of drug.

Bacterial genome sequencing and drug discovery.

The availability of bacterial genome sequence information has opened up many new strategies for antibacterial drug hunting. There are obvious benefits for the identification and evaluation of new drug targets, but genomic-based technology is also beginning to provide new tools for the downstream, preclinical, optimisation of compounds. The greatest benefit from these new approaches lies in the ability to examine the entire genome (or several genomes) simultaneously and in total. In this way, one potential target can be evaluated against another, and either the total effects of functional impairment can be established or the effects of a compound can be compared across species.

On the catalytic mechanism of prokaryotic leader peptidase 1.

The catalytic mechanism of leader peptidase 1 (LP1) of the bacterium Escherichia coli has been investigated by a combination of site-directed mutagenesis, assays of enzyme activity in vivo utilizing a strain of E. coli which has a conditional defect in LP1 activity, and gene cloning. The biological activity of mutant forms of E. coli LP1 demonstrates that this enzyme belongs to a novel class of proteinases. The possibility that LP1 may be an aspartyl proteinase has been excluded on the basis of primary sequence comparison and mutagenesis. Assignment of LP1 to one of the other three recognized classes of proteinases (metalloproteinases, thiol proteinases and the classical serine proteinases) can also be excluded, as it is clearly demonstrated that none of the histidine or cysteine residues within LP1 are required for catalytic activity. The Pseudomonas fluorescens lep gene has been cloned and sequenced and the corresponding amino acid sequence compared with that of E. coli LP1. The E. coli LP1 and P. fluorescens LP1 primary sequences are 50% identical after insertion of gaps. The P. fluorescens LP1 has 39 fewer amino acids, a calculated molecular mass of 31903 Da and functions effectively in vivo in E. coli. None of the cysteine residues and only one of the histidine residues which are present in E. coli LP1 are conserved in sequence position in the P. fluorescens LP1 enzyme. The possibility that LP1 is a novel type of serine proteinase is discussed.