Jansen Laboratory - Research
Structure and function studies of ligand-gated ion channels and transporters
Michaela Jansen's primary research focus are structure-function studies of membrane proteins on a molecular level. Additionally, we investigate mechanisms of drugs in current clinical use.
Methods used include a wide array of molecular biology (protein engineering), biochemical and biophysical (X-ray crystallography, electrophysiology) as well as chemical biology and pharmacology approaches .
One main focus are the so called Cys Loop receptors. These receptors function as neurotransmitter receptors. They transform the chemical signal contained in the neurotransmitter into an electrical
signal. The superfamily of Cys Loop receptors has a variety of members, that are named
after the ligand that opens (gates) them. They are virtually abundant in the central
and peripheral nervous system and our research is therefore considered Neuroscience.
These receptors were also identified in prokaryotes and we were the first lab to engineer
functional chimeras by adding the intracellular domain that is only found in eukaryotic receptors to
the proton-gated channel from Gloeobacter violaceus (GLIC).
||Clinically targeted for:
||Treatment of Nicotine addiction, Alzheimer's Disease
||Treatment of Epilepsy, Anaesthesia, Muscle relaxation, Anxiolytics
||5-hydroxytryptamine = serotonine
||Treatment of Depression, Nausea in Chemotherapy
Other members of the superfamily include receptors for glycine, zinc, glutamate, and
protons. Each receptor is made up of five subunits that are arranged pseudosymmetrically
around the central ion-conducting pore. These subunits can change their conformation
from closed (non ion conducting) to open (ion conducting) states.
||The overall topology of the individual subunits is comparable. The ~200 amino acid
long extracellular domain (ECD) harbors the ligand binding domain and the eponymous
13 amino acids bridging disulfide loop. Four alpha-helical segments (M1-M4) form the
transmembrane domain (TMD). Two short loops, one intracellular between M1 and M2 and
one extracellular between M2 and M3 connect the transmembrane domains. The large M3M4
loop is the major contributor to the intracellular domain (ICD). The intracellular
domain is reduced to a minimum in prokaryotic Cys Loop Receptors. We have shown that
the long M3M4 loop in 5HT3A and GABA rho1 can be replaced by just a heptapeptide linker found in GLIC while retaining
functionality. We have also generated the opposite chimeras between ECD and TMD of
GLIC and diverse eukrayotic ICDs.
||Homology Models of Eukaryotic and prokaryotic-like 5HT-3A receptors
||The structure and function of these receptors is studied in wildtype or engineered
receptors. Very often we engineer receptors by using site-directed mutagenesis to
selectively change one amino acid to a cysteine. In-vitro mRNA is synthesized by standard
molecular biological methods, injected into Xenopus laevis oocytes, and the function investigated in Two-electrode voltage clamp experiments
|Two-Electrode Voltage Clamp
||Setup for TEVC
||Heterologous overexpression and purification of membrane proteins. Biochemical studies
of membrane proteins. Crystallization trials of soluble and membrane proteins.
||Spectroscopy. Mass Spectrometry. Electrophysiology.
Michaela Jansen also uses other biophysical, protein engineering and biochemical
approaches to investigate these receptors.
Homology modeling of proteins is used to design new projects, visualize and explain
results, and for preparing figures for publications!
Ligands for Ion-Channels
Michaela Jansen is also interested in the development of glycine-site NMDA antagonists
(QSAR, ligands for PET), as well as the development of subtype selective GABAA receptor ligands.