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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.
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