TY  - UNPB
ID  - discovery17315
M1  - Doctoral
Y1  - 2009/02//
UR  - https://discovery-pp.ucl.ac.uk/id/eprint/17315/
A1  - Young, G.T.
PB  - UCL (University College London)
N2  - Nicotinic acetylcholine receptors (nAChRs) are members of the ligand-gated ion
channel family. They are also members of the sub-family of Cys-loop ligandgated
ion channels, which includes closely related receptors for the
neurotransmitters ?-aminobutyric acid (GABA), glycine, and 5-
hydroxytryptamine (serotonin).
There is a wealth of evidence demonstrating that nAChRs are involved in
mediating fast excitatory transmission, and also that they modulate the release of
other neurotransmitters. They have been implicated in several neurological
disorders such as Alzheimer?s disease, Parkinson?s disease, and schizophrenia,
and also mediate the effects of nicotine associated with tobacco smoking. They
are therefore viewed as potentially useful targets for the development of
therapeutic drugs.
In addition to the endogenous neurotransmitter acetylcholine, nAChRs are targets
for a diverse collection of naturally occurring ligands. These include agonists and
antagonists isolated from plants, freshwater algae, marine worms, frogs, the
venoms of snakes and predatory marine snails. An increasing collection of
synthetic ligands have also been produced which act upon the nAChR. The aim of
work presented in this thesis is to investigate recently developed ligands of the
nAChR and to characterise their action.
Work is presented aimed at characterising TMAQ, a ?4-selective nAChR agonist.
Strikingly, this agonist exhibits activity only upon nAChRs containing the human
?4 subunit whilst showing no activity on receptors containing the rat ?4 subunit.
Evidence is presented which, using hybrid receptors and chimeric subunits,
identifies the extracellular portion of the human ?4 subunit as being critical to this
species-selectivity. More specifically, the work demonstrates that a region of the
extracellular domain (loop D) of the ?4 subunit is responsible for this species selectivity. Additionally, it is shown that, although acting as an agonist of human
?4-containing nAChRs, TMAQ acts as an antagonist of rat ?4-containing
nAChRs. A homology model of the ?4 subunit is also presented which identifies
the location of the important residues; rationale is provided for their effects.
Work is also reported which characterises positive allosteric modulators of ?7
nAChRs, another class of nAChR ligand. Two classes of positive allosteric
modulators are examined utilising prototypes from each class. It was found that
type I positive allosteric modulators, such as LY-2087101, increase the magnitude
of peak response to agonists. Type II positive allosteric modulators, such as PNU-
120596, not only increase the magnitude of peak response to agonist but also slow
the receptor?s rate of desensitisation. Chimeric ?7/5HT3A subunits were used to
identify domains crucial to the site of action for PNU-120596; the first three
transmembrane domains were found to be essential. Mutation of individual
residues within the ?7 transmembrane domains into the equivalent amino acids in
the 5HT3A subunit identified several key residues. Homology modelling and
computational docking of allosteric modulators helped to support the theory that
these residues line the binding site for PNU-120596 and LY-2087101. Due to this
site?s similarity to modulatory sites found in other closely related receptors it is
argued that it represents a conserved modulatory site across the Cys-loop family
of receptors.
AV  - none
EP  - 212
N1  - Authorisation for digitisation not received
TI  - Molecular characterisation of nicotinic acetylcholine receptor subtypes: interactions with agonists and allosteric modulators
ER  -