Biology Reference
In-Depth Information
the haem-bound ligand and surrounding amino acid residues, which will be a
trigger of a conformational change in awhole protein. Conformational changes
of the protein play an important role for the regulation of the physiological
activity of the protein. Analyses of ligand binding-induced conformational
changes in detail are required to understand themolecular mechanisms of sens-
ing and signal transductions for the haem-based sensor proteins. As haem is a
very good spectroscopic probe, many spectroscopic techniques including laser
flash photolysis, ultraviolet/visible (UV-vis), resonanceRaman, electron para-
magnetic resonance (EPR), and extended X-ray absorption fine structure
(EXAFS) have been used to study the structure and function relationships of
the haem-based sensor proteins along with X-ray crystallography.
The haem-based sensor proteins can be categorised into several types based
on the differences of the domains accommodating haem. PAS, GAF,
H-NOX, CRP/FNR, and globin domains are known to be adopted as a sen-
sor domain accommodating a haem in the haem-based sensor domains. This
chapter focuses on the recent developments of the studies on the sensor pro-
teins containing a haem-containing PAS domain or several related domain.
2. GENERAL PROPERTIES OF PAS DOMAINS
PAS domain consists of ca. 100-120 residues, which is widely distributed
among Bacteria, Archaea, and Eukarya (
M¨glich, Ayers, & Moffat, 2009
).
Though the amino acid sequence homologies are not high among PAS
domains, their three-dimensional structures are similar. In most cases, PAS
domain(s) is a part of multi-domain proteins, where it plays a role for biological
signal transductions by signal sensing and/or by protein-protein interactions.
The canonical PAS fold shows the
a
/
b
structure consisting of five antiparalleled
b
strands (A
b
,B
b
,G
b
,H
b
,andI
b
) and four
a
helices (C
a
,D
a
,E
a
,andF
a
)
(
M¨glich et al., 2009
). Some PAS domains accommodate a prosthetic
group such as haem, flavin, or para-coumaric acid, which are used for sensing
external
signals
such as diatomic gas molecules and light
(
Henry &
Crosson, 2011
).
3. SINGLE-COMPONENT SYSTEMS FOR
TRANSCRIPTIONAL REGULATION
3.1. CO oxidation operon
There are two major systems to regulate biological functions in response to
external chemical or physical signals: single-component and two-component
