Two Component signal transduction as potential drug targets in pathogenic bacteriaYasuhiro Gotoh, Yoko Eguchi, Takafumi Watanabe, Sho Okamoto,Akihiro Doi and Ryutaro Utsumi

Curr Opin Microbiol, 2010, 13:232–239

Introduction• Bacteria respond different

environment signals• These signals can be pH,

Nutrient level, Redox state, Osmotic pressure, Quorum signals and antibiotics

• For this they use a two component signal transduction system (TCS)

• TCS is absent in mammals(including Homo sapiens)

• Hence these TCS can be targeted for drugs

Classic TCSHas

- Sensory kinase( Histidine kinase)(HK)Autophosphorylated on conserved His residue.Phosphoryl group transferred to RR.- Response regulator (RR)• Phosphorylated by HK at Asp

residue.• Phosphorylated RR binds to

upstream regulatory region of pathogenic genes and controls their expression.

• Dephosphorylated by HK.http://syntheticmicrobe.bio.lmu.de/research/signal_transduct/index.html

Molecular Mechanism of specific TCS

• TCS are involved in regulation 2 gene types- genes required for cell growth and is

essential- genes required for virulence in

pathogenic bacteria and are not essential.• These portions have the potential to serve as

effective drug targets

http://www.esrf.eu/news/spotlight/spotlight105/

Essential TCS• WalK/WalR TCS

Required for growth of pathogenic bacteria such as B. subtilis, S. aureus, E. faecalis, L. monocytogenes, S. pneumoniae, S. mutans, S. pyogenesMostly involved in cell wall metabolism, biofilm formation etc.

Inhibitors of WalK/WalR TCS• Inhibitors of this pathway identified by

differential growth assay and homodimerization assay. They were walkmycin B and walrycin B respectively

• Other inhibitors were thiazolidinone derivatives against S. epidermidis identified by virtual screening of small molecule lead-compound library.

Non Essential TCS• Virulence factors such as toxins, proteases, lipase

are required for host invasion, other properties required are motility, adherence to host, colonization.

• These factors and properties are controlled by TCS where the host environmental factors activate these systems.

E.g. P. aeroginosa has 64 HKs and 72 RRs out of which 19 are involved in virulence and antibiotic resistance

QseC/QseB• E.Coli [EHEC] causative agent of

bloody diarrhea and hemolytic-uremic syndrome use this TCS for virulence.

• By quorum sensing, chemical autoinducer (AI-3)is produced that rapid induce virulence gene LEE.

• LEE gene expressed during high concentrations of human hormones epinephrine and norepinephrine.

• QseC/QseB TCS regulates flagella regulon and LEE gene shiga toxin.

• Inhibitor LED209 supressed pathogenic genes LEE1,flhDC and stx2A and inhibited auto phosphorylation of QseC

AgrC / AgrA• S. aureus an oppurtunistic

pathoges has its virulence controlled by TCS AgrC/AgrA that regulates virulence factors

• AgrD is an AIP [autoinducing cyclic thiolactone peptides] that is processed by AgrB that is present in the cell membrane.

• Processed AIP are sensors for AgrC/AgrA TCS.

• Inhibitors include noncognate AIPs and apolipoprotein.

FsrC/FsrA• Multiple antibiotic resistant E. faecalis causes

opportunistic nosocomial infections.• Virulence factors gelatinase and serine protease

coded by genes gelE and sprE are present in the same operon

• They depend on concentration of GBAP ( gelatinase biosynthesis-activating pheromone) i.e secreted outside the cell

• GBAP production positively controlled by FsrC/FsrA TCS that in turn trigger FsrC/FsrA controlling expression of genes fsrBDC and gelE-sprE.

• Inhibitors from mycetal extracts were identified, Siamycin I (peptide).

GacS/GacA• P. aeruginosa depends on

this TCS for their virulence in nosocomial infections.

• Virulence factors like acyl homoserine lactones,pyocyanin,lipase,elastase etc are involved whose transcription is indirectly controlled by GacS/GacA TCS

• E.carotovora causes soft rot disease in plants when there is GacS/GacA mediated production of rsmB gene product

Environmental microbiology –Ralph mitchell

PhoQ/PhoP• Regulates Salmonella’s ability to invade epithelial

cells, survive in phagocytic cells and resist AMPs• PhoQ sensor detects extracellular Mg+2

concentration and mediates expression of 3% of salmonella genes by PhoP

• Inhibitors include GHL inhibitors such as Radicicol that bind to ATP binding Bergerat fold.

• This TCS is also present in E. caratovora called PehS/PehR that regulates endopolygalacturonase required for virulence.

CorS/CorRP.Syringae caused chlorosis due to

phytotoxin coronatine

HrpX/HrpYE. amylovora’s Type III secretion system (T3SS) controlled by this system and detected by low pH, low nutrient level, low temperature.Inhibitor identified – p – coumaric acid

Conclusion• Sensory domains are the main drug targets in TCS• Development of drugs targeting other conserved

domains to act on pathways involving multiple TCSs• HK inhibitors showed poor selectivity of TCS and

damaged membranes of cells• TCS inhibitors to be developed covering their broad

range and has to be highly specific to them.• These inhibitors can be new antibiotics against

multidrug resistant pathogens and antivirulence agents for pathogens without essential TCS.