Chemistry Reference
In-Depth Information
7
Studying the Dynamics of Ligand
Receptor Complexes
-
by Single-Molecule Techniques
Christophe Danelon and Horst Vogel
7.1
Introduction
The speci
c recognition and binding betweenmolecules is fundamental to biological
function. The
first step in essentially all cellular signaling activities is the interaction
between a ligand and a protein to form a de
ned complex that triggers downstream
intracellular reactions.
Here, we will focus on ligand
-
receptor interactions on cellular membranes. Signal
transduction across cellular membranes relies on a complex biochemical network
involving chemical or physical stimuli, membrane receptors and cytosolic proteins.
The signal initiated by ligand binding is transduced across the receptor protein to
modulate subsequent interactions on the opposite side of themembrane. Membrane
receptors can be classi
ed on the basis of the mechanism by which they transfer the
information:
(i) G protein-coupled receptors (GPCRs) mediate the detection of photons or
diverse chemical compounds such as hormones, neurotransmitters,
odorants, and nucleosides [1] to the activation of G proteins located on the
cytosolic face of the plasma membrane, which
finally stimulate other membrane
effectors. Rhodopsin, opioid receptors, olfactory receptors are prototypical
representatives of GPCRs.
(ii) Ion channels and transporters allow the translocation of ions or molecules across
cellular membranes. Ligand-activated ion channels expose one or several af
nity
sites for agonistmolecules, the bindingof which gates the channel to anopen state
for speci
c ions [2]. The ligand can be extracellular such as a neurotransmitter, or
intracellular e.g. a cyclic nucleotide or inositol-3-phosphate. There is another type
of receptor channels that comprise a binding site at the interior of the pore. These
include speci
c bacterial channels which have been studied in detail with regard
to the translocation mechanism.
