Target-Based Antimicrobial Drug Discovery - Bacterial Pathogenesis: Methods and Protocols - page 260

have yet to yield agents with antibacterial activity but further an understanding
of potential sites for disruption of the pathway.
3.7. Well-Defined Complex Macromolecules-New Looks at Old
Friends
DNA replication and the complex structural and catalytic components
involved remain clear targets for new antimicrobial efforts and numerous
researchers are investigating them. Recently, a number of novel and selective
inhibitors of DNA polymerase III in Gram-positive bacteria have been described
in the literature. A recent report describes the use of hexapeptides that theoreti-
cally bind to the Holliday junctions formed during DNA repair (28) . Treatment
with the hexapeptides appears to inhibit resolution of the junctions and results
in accumulation of DNA breaks, leading to filamentation, erroneous DNA parti-
tioning, and anucleate cells. Researchers demonstrated antimicrobial activities
associated with these inhibitors in vitro but to date have not tested them in
animal models. Nevertheless, they suggest that the inhibitors might be useful
either as antimicrobial agents alone or in combination or at least as tools to aid
in understanding DNA repair.
It is widely believed that as the structure of the translational machinery is
elucidated even further, the ribosome will yield even more opportunities for
antimicrobial intervention (21) . Moreover, other enzymes required for efficient
and accurate protein synthesis are being investigated as targets. Aminoacyl
tRNA synthetases are essential enzymes required for the charging of tRNAs
with their respective amino acids. Because the catalytic mechanism is well
understood, the design of substrate or reaction-intermediate mimics can be
utilized (29) . Both natural product and synthetic libraries have been screened
for inhibitors and have yielded multiple candidate inhibitors. While many have
demonstrated significant activity in vitro, limited success has been demonstrated
to date against whole cells, once again highlighting the challenge of translating
enzymatic inhibition into actual antibacterial activity. However, limited reports
of activity in infection models maintain interest in these enzymes for use as
chemotherapeutic targets.
Another target of great interest in the protein synthetic pathway is peptide
deformylase (30,31) . This metalloenzyme is required for the removal of the
N-terminal formyl group of newly synthesized proteins. This process is absent
in eukaryotes, and hence this enzyme is an attractive target. Several peptide
deformylase inhibitory compound series have been identified, some exhibiting
activity in animal models, suggesting that this target might prove fruitful in the
search for novel antimicrobials.