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Bacterial resistance to antibiotics poses an unprecedented challenge to global health.
In search of novel antibacterial strategies capable of evading existing resistance mechanisms,
we identified the bacterial signal recognition particle (SRP), an essential protein transport
machinery, as a potential target. Functional SRP is composed of a protein (Ffh) and a 4.5S
RNA component, so we envisioned that antisense peptide nucleic acid (PNA) molecules
targeting 4.5S RNA might inhibit the RNA-Ffh interaction, thus compromising bacterial
viability. Designed PNA molecules indeed bound specifically to 4.5S RNA, and inhibited the
4.5S RNA-Ffh interaction in a dose dependent manner, leading to inhibition of SRP mediated
GTP hydrolysis. The most potent PNA molecule, when tagged with a cell penetrating
peptide, was able to effectively inhibit E. coli cell growth. The PNA-mediated inhibition was
relieved by overexpression of 4.5S RNA, suggesting that the PNA specifically blocks 4.5S
RNA function. Our work validates SRP as an antibacterial target for the first time, and invites
research into small molecule inhibitors of bacterial SRP as potential antibacterial agents.
Molecular chaperones play an essential role in maintaining proteostasis in the cell.
The bacterial chaperone DnaK, a homologue of heat shock protein (Hsp70), actively holds or
unfolds thermosensitive proteins and prevents their misfolding and aggregation. DnaK is
essential under stress, and is thus an attractive antibacterial target. Using an in-house small
molecule library screening approach, we identified a synthetic molecule M7 as a potential
inhibitor of DnaK. Competitive binding studies with a substrate peptide suggest that M7
likely binds at the DnaK substrate-binding domain, and inhibits ATPase and luciferase
refolding activity of DnaK. We find that M7 inhibits P. aeruginosa growth and biofilm
formation. SEM and confocal imaging suggest that M7 could permeate bacterial cells and
inhibit growth, while itself being non-toxic to HEK cells. Thus, M7 is a promising lead for
DnaK inhibition. |