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Whats new?
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| In collaboration with Prof. Heilmann from the Department of Pharmaceutical Biology
we have established an Sf9 insect cell expression system for human
cannabinoid receptors 1 and 2. In a study recently published in
Neuroscience Letters (see Abstract) we show differential coupling of the two receptors to the G-protein Gai2. This expression systems provides us with a basis for the pharmacological receptor characterization. |
Our laboratory is very interested in the concept of
ligand-specific receptor conformations. During the past 3 years, we
have focused on the histamine H1- and H2-receptor.
More recently, we have come back to the beta-adrenergic receptors that
we had studied in detail from 1995-2003. In a recent study (see Abstract)
we have unmasked substantial differences in the interactions of the
endogenous catecholamines epinephrine, norepinephrine and dopamine with
b1- and b2-adrenergic
receptors. Our current results support previous functional data form
our laboratory with isoproterenol, dobutamine, salbutamol,
dichloroisoproterenol and ephedrine and fluorescence spectroscopy
studies from the Kobilka laboratory, strongly supporting the existence
of such ligand-specific receptor conformations. We also discuss the
potentially broad clinical implications of our data.
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| In contrast to the data obtained with the H2-receptor, the second extracellular loop does play a role in determining the pharmacological properties of the H1-receptor.
Combining radioligand binding studies, steady-state GTPase assays,
site-directed mutagenesis and molecular modelling based on the novel
crystal structure of the b2-adrenergic receptor, we have obtained evidence for a role of the second extracellular loop of the H1-receptor
on affinity and/or potency of histamine and a specific class of
synthetic ligands, the phenoprodifens.The results of this research
project have been published in J Pharmacol Exp Ther (see Abstract). |
In collaboration with the group of Dr. Schäferling
from the Institute of Analytical Chemistry of the University of
Regensburg and the group of Dr. Tang from the University of Chicago, we
have developed a novel terbium norfloxacin-based real-time adenylyl
cyclase assay. This sensitive assay allows for the detailed kintic
analysis of adenylyl cyclase activity without the need for radioactive
substrate and educt/product separation by column chromatography. Since
the assay can be conducted in small reaction volumes using a plate
reader, it has the potential for high-throughput screeing of novel
adenylyl cyclase inhibitors. In the paper published in Analytical
Biochemistry (see Abstract),
we have used the adeynylyl cyclase toxin from Baciluus anthracis, edema
factor, as paradigm to comapre the results of the fluorescence assay
with the standard radioactive assay.
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| In a collaboration with the Departments of Pharmacology
and Medicinal Chemistry of the University of Kansas we have established
a very sensitive reconstitution system for the human chemokine receptor
CXCR4. This system will facilitate the development of CXCR4 antagonists
that are of potential value for the treatment of autoimmune diseases,
certain tumors and HIV infection. Moreover, the study revealed that
CXCR4, unlike related receptors, lacks constitutive activity and
preferentially couples to the G-proteins Gai1 and Gai2. This research was published in Naunyn-Schmiedeberg's Arch Pharmacol (Abstract). |
To this end, our adenylyl cyclase research has focused
on the analysis of fluorescent nucleotides as inhibitors and
conformational probes. As a new direction of the adenylyl cyclase
project, we are now also studying the interaction of the enzyme with
forskolin analogues. This project is conducted as an interdisciplinary
project involving biochemical, pharmacological, chemical, molecular
modelling and crystallographic approaches. The project is being
performed at three institutions, i.e. the University of Regensburg, the
University of Kansas and the University of Montana. In the first
publication emerging from this project published in J. Pharmacol. Exp. Ther.,
we describe differential activation and inhibition of adenylyl cyclase
isoforms by non-fluorescent and fluorescent forskolin analogues. Our
data provide evidence for the existence of multiple active and inactive
adenylyl cyclase conformations.
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| Wir are continuing our collaboration with the group of Prof. Dr. Armin Buschauer on the molecular analysis of the histamine H2-receptor. Since the human and the guinea pig H2-receptor
show structural differences in the second extracellular loop, we asked
the question whether those differences may affect the pharmacological
profile of the rececptors, particularly with respect to interaction
with bulky guanidine-type agonists. In fact, for other biogenic amine
receptors, a role of the second extracellular loop in ligand binding
has been suggested. By using site-directed mutagenesis, molecular
modelling and molecular pharmacology approaches, in a study recently
published in Naunyn-Schmiedeberg's Archives of Pharmacology (see Abstract) we show that the second extracellular loop does NOT participate in ligand binding at H2-receptors.
However, our data do not exclude the possibility that with other as not
yet studied ligands, the second extracellular loop does participate in
ligand recognition. |
In addition to the H2-receptor, we are also very interested in the molecular pharmacology of the H1-receptor. The H1-receptor
plays a key role in mediating acute allergic reactions. In an
interdisciplinary study using medicinal chemistry, molecular
pharmacology, molecular biology and molecular modelling approaches, we
provide evidence for the notion that a new class of H1-receptor
agonists, the chiral histaprodifens (chiraprodifens) interact in very
distinct manners with four species isoforms of the H1-receptor (see Abstract and FastForward-Publication).
Particularly, we observe species-specific agonistic and antagonistic
properties of chiraprodifen isomers among the receptor isoforms. This
study provides the basis for future studies in our group in which we
will aim at elucidating the precise structural basis for the
pharmacological differences between the receptor isoforms.
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