Biology Reference
In-Depth Information
signal transduction systems. In the single-component signal transduction sys-
tem, the same protein shows the functions of not only sensing external signals
but also regulating biological functions. For example, transcriptional regula-
tors that consist of a sensor and DNA-binding domains are typical for the
single-component system. In this system, conformational changes are induced
upon sensing the cognate effector molecule/signal by the sensor domain,
which ends up with regulation of the DNA-binding activity.
CO oxidation operon (CooA) protein is a single-component transcrip-
tional regulator, which is one of the most widely studied haem-based sensors
( Aono, 2003, 2011; Roberts et al., 2005 ). CooA consists of the N-terminal
CRP/FNR-like sensor domain and the C-terminal DNA-binding domain
( Komori, Inagaki, Yoshioka, Aono, & Higuchi, 2007; Lanzilotta et al.,
2000 ). A b-type haem in the sensor domain acts as the active site for sensing
CO ( Aono, Nakajima, Saito, & Okada, 1996 ). The haem in CooA shows a
dynamic change in the coordination structures of the haem. While the ferric
haem in CooA from Rhodospirillum rubrum (Rr-CooA) is coordinated with
Cys75 and Pro2, a ligand exchange takes place between Cys75 and His77
upon reduction of the haem ( Fig. 7.1 ; Aono, 2003, 2011; Aono,
Ohkubo, Matsuo, & Nakajima, 1998 ). This redox-dependent ligand
exchange is fully reversible reaction. Though the ferrous haem in
Rr-CooA is coordinationally saturated with two endogenous axial ligands,
it can bind CO to form CO-bound haem under physiological conditions,
during which the ligand exchange takes place between Pro2 and CO
( Aono, 2003; Nakajima et al., 2001; Yamamoto et al., 2001 ).
Pro2
Pro2
CO
Fe 3+
Fe 2+
Fe 2+
Cys75
His77
His77
B RcoM2
C ys94
Me t104
CO
Fe 3+
Fe 2+
Fe 2+
His74
Figure 7.1 Coordination structures of the haem in (A) Rr-CooA and (B) RcoM2.
Search WWH ::




Custom Search