Lecture 10 1
2 Component Systems II
There is a wide array of different biological processes
controlled by 2 C systems.
The number of 2C systems in each bacterial species is
Mycoplasma spp. : 0 (intracellular pathogen) Bacillus subtilus: 34 sets
Haemophilus influenzae : 5 HPK; 4 RR Synechocystis : 38 sets
E. coli : 28 sets Pseudomonas: 63 HPK; 64 RR
But proteins with limited homology have been identified in
Archea, Plants, Yeast, & mammalian mitochondria
Thus, the phosphotransfer RXNs catalyzed by HPK & RRs
represent an ANCIENT evolutionary signaling mechanism.
Archaeal and eukaryotic 2CS have evolved through
separate horizontal transfers of bacterial genes.
Eukaryotic = hybrid type
Archaea = classical
44 RRs: 24 = OmpR-
like; 12 = FixJ-like; 8
20 others: Lecture 10 2
4 = CheB-like (output domain = esterase activ)
5 = CheY-like (no output domain)
11 = new RRs with conserved receiver domains, but
output domains unrelated to known RR’s / each other
63 HPKs: 42/63 are classical IT > RR
5 = CheA-like (transmitter domain near N-term), Hpt-like
5 = Unorthodox: gene fusion with histidine-containing
phosphotransfer module (Hpt): ITRHpt > RR Lecture 10 3
11 = Hybrid: these don’t contain an extended C term in
receiver domain; phosphorelay between HPK & RR occurs
with a separate Hpt module (dif protein) ITR > Hpt > RR
Hpt module proteins – only 3 found in Pa. Genome / But
2/3 are found next to orphaned RR genes (orphaned
genes do not have a known partner at that site on the
genome. E.g. no sensor kinase at that site on the
Cognate HPK and RR pairs are usually found on genes
located next to each other ; sometimes same Tn unit.
Classical 2C genes function in same signaling pathway
Predicts that orphaned atypical 2C genes function with
more than one partner ie CROSSTALK
The high number of atypical 2C systems is unique to Pa.
(involved in 4 step phosphorelay)
Maybe these offer checkpoints for phosphorylation rates Lecture 10 4
Phosphorylation Rate – controlled at
1. RR level – by specific phosphatases
2. at receiver module of RR by other more general
3. Reverse Phosphorelay
4. In Pa., there are 11 HPK that seem to require Hpt
modules, but there are only 3 Hpt modules. Bottleneck.
How can this work?
1. There are other unknown Hpts with different AA
2. Maybe phosphoryl transfer does not always
require an Hpt molecule. This would be unusual. Lecture 10 5
3. There are known examples where many hybrid
kinases use the same Hpt.
1. High number of 2C systems in Pa.
2. 16 atypical HPK (His-Asp phosphorelay) allows
multiple regulatory checkpoints.
3. A 4 step phosphorelay by 3 proteins permits crosstalk
4. Different phosphatase members acting = lots of
Potential targets for Antimicrobial Therapy
1. 2C systems are widespread in bacteria, absent in
2. by targeting select HKs or RRs, selective inhibition
may be achieved (1 antibiotic broad spectrum)
Problem – most 2C systems are non-essential.
BUT if you could shut down a few, due to their inter-
dependence, you may be able to effect cellular shut-down
3. 2C systems are used by pathogenic bacteria to
control expression of virulence factors.
e.g. B pertussis BvgAS; S typhimurium PhoPQ. And
resistance to antibiotics: S pneumoniae VncSR vancomycin