Biology Reference
In-Depth Information
Figure 7.11 Crystal structures of the periplasmic PAS domain of (A) GSU0582 (PDB
3B47) and GSU0953 (PDB 3B42).
The ligand exchange takes place upon the reduction between the haem-
bound water molecule and Met60 to form the ferrous haem with two
endogenous residues as the axial ligands. In the structure of GSU0935,
the coordination structures of the haems in two protomers are different from
each other. For the haem of chain B, it is in high-spin state with His144 and a
water molecule as the axial ligands. The haem-bound water molecule has a
hydrogen-bonding pattern similar to that observed in GSU0582. The haem
of chain A is in 6-coorinate and low-spin state with His144 and Met60.
GSU0582 and GSU0935 show EPR spectra with
g
5.90 and 5.93,
respectively, characteristic of high-spin haems with
S¼
5/2. While the
high-spin signals are predominant in both cases, a trace amount of low-spin
haem (
S
¼
1/2) is also observed at
g
values of 2.28 and 2.75, and 2.28 and
2.81 for GSU0582 and GSU0935, respectively, which suggest an equilib-
rium between low-spin and high-spin states (
Pokkuluri et al., 2008
). In
the resonance Raman spectra, ferric GSU0582 and GSU0935 show two
¼
