Biology Reference
In-Depth Information
The binding of an external ligand to a 6-coordinated haem with ligand
exchange will induce a large conformational change around the protein
main chain at which the residue dissociated from the haem, which can be
a trigger for conformational changes responsible for the functional regula-
tion of proteins. In the case of Rr-CooA, Pro2 bound to the ferrous haem
is dissociated from the haem iron upon CO binding (
Aono, 2003; Nakajima
et al., 2001; Yamamoto et al., 2001
). As the N-terminus (Pro2) is bound to
the haem in the ferric and ferrous Rr-CooA, the conformation of the
N-terminal region in Rr-CooA is fixed. Upon CO binding to Rr-CooA,
relocation of the N-terminal region is induced by the dissociation of Pro2
from the haem, which causes conformational changes of the DNA-binding
domain, resulting in the activation of Rr-CooA for DNA binding (
Aono,
2003, 2011
).
3.2. Regulator of CO metabolism
Though CO concentration present in the natural environment is less than
1 ppm, a number of microbes express distinct CO-regulated systems includ-
ing CO-dependent transcriptional regulators and proteins responsible for
CO metabolism (
King &Weber, 2007; Ragsdale, 2004
). Two homologous
proteins, RcoM1 and RcoM2 from
Burkholderia xenovorans
, function as
CO-dependent transcriptional regulators, which consist of an N-terminal
PAS domain and a C-terminal LytTR family DNA-binding domain
(
Kerby, Youn, & Roberts, 2008
). The
rcoM1
gene in
B. xenovorans
is adja-
cent to the
coxMSL
genes encoding an aerobic CO oxidation system,
suggesting that RcoM1 is a regulator of the
cox
expression.
In vivo
assays
using
lacZ
fused to the promoter of the
coxM
as a reporter gene show that
RcoM1 and RcoM2 activate the expression of the reporter gene only in
the presence of CO (
Kerby et al., 2008
).
The N-terminal PAS domain binds a b-type haem in RcoM1 and
RcoM2 (
Smith et al., 2012
). Amino acid sequence alignments reveal that
the proximal His (His74 in RcoM) is conserved among regulator of CO
metabolism (RcoM), FixL, and
Ec
Dos. RcoM1 shows the Soret,
a
, and
b
bands at 420, 574, and 539 nm; 426, 562, and 531 nm; 423, 570, and
540 nm; and 421, 578, and 545 nm in the ferric, ferrous, ferrous-CO,
and ferrous-NO forms, respectively (
Kerby et al., 2008
). RcoM2 shows
similar UV-vis spectra to those of RcoM1, and its detailed spectroscopic
properties are studied by EPR, MCD, and resonance Raman spectroscopy
(
Marvin, Kerby, Youn, Roberts, & Burstyn, 2008
). Ferric RcoM2 shows
