Abstract
The main components of the quorum-sensing system are expected to be favorable targets for drug development to combat various chronic infectious diseases. ComA of Streptococcus is an ATP-binding cassette transporter containing a peptidase domain (PEP), which is essential for the quorum-sensing signal production. Using high-throughput screening, we found a potent small molecule that suppressed the S. mutans quorum-sensing pathway through inhibition of PEP activity. The compound effectively attenuated the biofilm formation and competence development of S. mutans without inhibiting cell growth. The kinetic and structural studies with this molecule and a related compound unexpectedly revealed an allosteric site of PEP. This relatively hydrophobic site is thought to undergo large structural changes during the catalytic process. These compounds inhibit PEP activity by binding to and suppressing the structural changes of this site. These results showed that PEP is a good target for inhibitors of the Streptococcus quorum-sensing system.
Highlights
ComA is a bi-functional ATP-binding cassette (ABC) transporter that comprises three domains: an N-terminal peptidase domain (PEP), a transmembrane domain, and a C-terminal nucleotide-binding domain[13,14,15]
S. cristatus ComC (CComC) was used because S. mutans ComC could not be chemically synthesized and CComC was a good substrate of MuPEP117
After the inhibitory activities of the selected compounds were re-evaluated by high-performance liquid chromatography assay, dose-dependent inhibition against MuPEP1 was examined in a second screening that yielded 110 compounds with IC50 values of
Summary
ComA is a bi-functional ATP-binding cassette (ABC) transporter that comprises three domains: an N-terminal peptidase domain (PEP), a transmembrane domain, and a C-terminal nucleotide-binding domain[13,14,15]. We believe that PEP of ComA is a more suitable target for inhibitor development for the following reasons: First, PEP catalyzes the initial step of the quorum-sensing system of Streptococcus. Among ubiquitous ABC transporters, ComA-like transporters equipped with the peptidase domains are found only in prokaryotes, minimizing the possibility of unpredictable adverse effects[13]. Because, as far as we have been able to determine, all streptococcal PEPs have a common substrate recognition mechanism[17], it may be possible to develop a quorum-sensing inhibitor that is effective for a range of streptococcal species in which PEPs play an important role in the quorum-sensing system. We set out to screen a library of small compounds for the inhibitory activity against S. mutans PEP (MuPEP1) by high-throughput screening
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