Biology Reference
In-Depth Information
DGC, induces biofilm formation (
Pesavento & Hengge, 2009; Seshasayee,
Fraser, & Luscombe, 2010; Tamayo et al., 2007
). These results suggest that
Lp
H-NOX1 is a NO sensor protein that regulates the DGC activity of
Lpg1057 encoded in the same operon with
Lp
H-NOX1.
5.2. PDEs consisting of a haem-containing PAS and EAL
domains
5.2.1 Spectroscopic properties of EcDos
Ec
Dos contains 807 amino acid residues, which consists of three domains,
two N-terminal PAS and C-terminal EAL domains. It contains one proto-
haem per monomer and the haem is bound to the first PAS domain. Ferric
and ferrous
Ec
Dos show the Soret and Q-bands at 416, 539, and 564 nm, and
427, 532, and 563 nm, respectively (
Delgado-Nixon, Gonzalez, & Gilles-
Gonzalez, 2000
). Resonance Raman spectra show the
n
2,
n
3, and
n
4 bands
at 1576, 1505, and 1370 cm
1
, and 1580, 1493, and 1361 cm
1
in ferric and
ferrous
Ec
Dos, respectively (
Tomita et al., 2002
). These spectra indicate that
the ferric and ferrous haems in
Ec
Dos are 6-coordinate, low-spin state.
Diatomic gas molecules such as O
2
, CO, and NO can be bound to the
haem in
Ec
Dos. O
2
-, and CO-bound
Ec
Dos show the Soret and Q-bands at
417, 541, and 579 nm, and 423, 540, and 570 nm, respectively (
Delgado-
Nixon et al., 2000
). The
n
(Fe-CO) and
n
(C-O) bands are observed at
487 and 1969 cm
1
, suggesting that the proximal ligand
trans
to CO is a neu-
tral His in CO-bound
Ec
Dos (
Tomita et al., 2002
).
The frequency of the
n
(Fe-O
2
) band is shifted by the change in the pat-
tern of hydrogen-bonding interactions to the haem-bound O
2
. When the
hydrogen bond to the proximal oxygen atom of the haem-bound O
2
exists,
the lower frequency of the
n
(Fe-O
2
) band is observed compared with the
O
2
-bound haem having the hydrogen bond to the distal oxygen atom (
Das,
Couture, Ouellet, Guertin, & Rousseau, 2001; Mukai, Savard, Ouellet,
Guertin, & Yeh, 2002; Yeh, Couture, Ouellet, Guertin, & Rousseau,
2000
). For example, while the
n
(Fe-O
2
) band appears at ca. 570 cm
1
in
Mb and Hb where a hydrogen bond exists between the distal oxygen atom
of the haem-bound O
2
and the distal His, it downshifts to 562 cm
1
in the
case of
M. tuberculosis
HbN where the hydrogen bond exists at the proximal
oxygen atom (
Ouellet, Milani, Couture, Bolognesi, & Guertin, 2006
). In
O
2
-bound
Ec
Dos, the
n
(Fe-O
2
) band is observed at 562 cm
1
(
Tomita
et al., 2002
), suggesting that a hydrogen bond to the proximal oxygen atom
exists in
Ec
Dos.