MOLECULAR SWITCHES Seminar Bioorganik (WS18/19) Leipzig, 28.01.2019
MOLECULAR SWITCHES
Seminar Bioorganik (WS18/19)
Leipzig, 28.01.2019
INTRODUCTION
Molecular switches
OPTOGENETICS
3
= technique to control cells in living tissue (typically
neurons) by light
Cells were genetically modified to express light-sensitive
ion channels
Optochemical genetics → addition of a chemical
component
Molecular switches
4
transmembrane proteins, sensitive to an input signal:
Light intensity
Pressure
Voltage
Temperature
Ligand concentration
all can be influenced by ligands (e.g. channel blockers)
→ point of contact for optochemical genetics
TRANSMEMBRANE RECEPTORS IN
NEUROBIOLOGY
Molecular switches
TRANSMEMBRANE RECEPTORS IN NEUROBIOLOGY
5
Activated by / ligand / voltage
Molecular switches
NEUROTRANSMISSION
6
Molecular switches
CHANNELRHODOPSIN-2
7
Molecular switches
LIGHTING UP THE BRAIN – LIGHT-SENSITIVE
RECEPTORS
8
→ Optogenetics
Fast modulation of intensity within femtoseconds
Can be focused onto very small areas
Carry enough energy to trigger larger molecular motions
MOLECULAR TOOLS
IN OPTOCHEMICAL
GENETICS
Molecular switches
CAGED LIGAND APPROACH (CL)
10
Simplest and oldest approach
first shown in living animals
Irreversible process and produces by-products
Molecular switches
PHOTOCHROMIC LIGAND APPROACH (PCL)
11
Ease of application, fast distribution → good as drugs
Work well in complex systems
Selectivity between receptor subtypes is challenging
Molecular switches
PHOTOSWITCHED TETHERED LIGAND
APPROACH (PTL)
12
Selectivity between receptor subtypes
Can be genetically encoded → biologic, not synthetic
Ligand does not need high affinity
Molecular switches
PTL – FUNKTIONAL DISSECTION OF RELATED
RECEPTOR SUBTYPES
13
Molecular switches
AZOBENZENE PHOTOSWITCHES
14
Fast, photostable, need low intensity
Easy to synthesize and modify
Low solubility → overcome with functional groups
VOLTAGE-GATED
POTASSIUM
CHANNELS
Molecular switches
VOLTAGE-GATED POTASSIUM CHANNELS
Modulate cellular excitability
Play a key role in the generation of action potentials
16
Molecular switches
VOLTAGE-GATED POTASSIUM CHANNELS
Channel blockers
Cs+ ions
Venom peptides
Small organic cations
External TEA
Internal TEA
17TEA: tetraethylammonium
Molecular switches
PHOTOSENSITIZING VOLTAGE-GATED
POTASSIUM CHANNELS
PTL approach
H-SPARK
Hyperpolarizing effect
18SPARK: Synthetic photoisomerizable azobenzene-regulated K+ channel
MAQ: maleimide/azobenzene/quartenary/ammonium
Molecular switches
PHOTOSENSITIZING VOLTAGE-GATED
POTASSIUM CHANNELS
PTL approach
D-SPARK
Depolarizing effect
19SPARK: Synthetic photoisomerizable azobenzene-regulated K+ channel
Molecular switches
PHOTOSENSITIZING VOLTAGE-GATED
POTASSIUM CHANNELS
PCL approach
XAQs
20
Molecular switches
PHOTOSENSITIZING VOLTAGE-GATED
POTASSIUM CHANNELS
Shift the absorption and action spectra toward the red
deeper tissue penetration
diminish the phototoxity
21
IONOTROPIC
GLUTAMATE
RECEPTORS
Molecular switches
IONOTROPIC GLUTAMATE RECEPTORS
Play a cenral role in synaptic transmission
Antagonists
„foot-in-the-door“ mechanism
23
Molecular switches
PHOTOSENSITIZING IONOTROPIC GLUTAMATE
RECEPTORS
PTL approach
LiGluR
24LiGluR: light-gated ionotropic receptor
Molecular switches
PHOTOSENSITIZING IONOTROPIC GLUTAMATE
RECEPTORS
Sign inversion
MAG-0 is attached to
25
cis activation
trans activation
Molecular switches
PHOTOSENSITIZING IONOTROPIC GLUTAMATE
RECEPTORS
HyLighter
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K+ selective TMD of the
procaroytic glutamate
receptor
Photosensitive LBD of
LiGluR
Molecular switches
PHOTOSENSITIZING IONOTROPIC GLUTAMATE
RECEPTORS
Controlling the escape reflex in zebrafish
27
Molecular switches
PHOTOSENSITIZING IONOTROPIC GLUTAMATE
RECEPTORS
PCL approach
28
PENTAMERIC LIGAND-
GATED ION CHANNELS
29
Molecular switches
SUBGROUPS
Nicotinic acetylcholine receptor (nAChR)
γ-aminobutyric acid receptors (GABAA/C)
5-hydroxytryptamine receptors (5-HT3)
glycine receptors (GlyRs)
30
acetylcholine
GABA
serotonin
glycine
Molecular switches
NICOTINIC ACETYLCHOLINE RECEPTOR
31Source: Nasiripourdori, A.; et al.: From Toxins Targeting Ligand Gated Ion
Channels to Therapeutic Molecules. Toxins. December 2011, 3:260-293
Molecular switches
Source:
NICOTINIC ACETYLCHOLINE RECEPTOR
32
• first photosensitized
receptor
• easy accessable in
certain fishes
acetylcholine
or
nicotin
Electrophoruselectricus
Source: https://de.wikipedia.org/wiki/Zitteraal#/media/File:Electrophorus_electricus_3.jpg,
18.01.19
Molecular switches
PHOTOSENSITIZING OF NICOTINIC
ACETYLCHOLINE RECEPTOR
33
PCL
PTL
OUTLOOK
Molecular switches
ALTERNATIVE AND FUTURE TARGETS FOR
PHOTOSENSITIZING
• countless receptors
• taste and olfactory receptors, GPCRs, etc.
• receptor linked enzymes
• e. g. receptor tyrosine kinases
• receptor agonists and antagonists
35
Molecular switches
PHOTOACTIVATABLE CHEMOKINES
36Source: Baumann, L.; Beck-Sickinger, A. G.: Photoactivatable Chemokines – Controlling Protein
Activity by Light. Angewandte Chemie. June 2013, Volume 52, Issue 36
Molecular switches
FUTURE TASKS AND UTILISATIONS
• phoswitchable cross-linkers
• exploring of new photoswitchers
• switchers sensitive für other signals
• orthogonal ligands
• electromagnetic fields
• knock-in instead of knock-out
mutants
37Source: Valeur, E.; et al.: New Modalities for Challenging Targets in Drug Discovery. Angewandte
Chemie. February 2017, Volume 56, Issue 35
Molecular switches
CURING BLINDNESS
38Source: https://www.allaboutvision.com/resources/retina.htm (20.01.19)
THANK YOU FOR YOUR
ATTENTION!