G protein-coupled receptors (GPCRs) are a
ubiquitous family of transmembrane molecules
that act as sensors for extracellular stimuli
including hormones, neurotransmitters, and
sensory stimuli such as light and smell. GPCRs
are characterized by their conserved structure
of seven transmembrane-spanning helices, as well
as extracellular N-terminal and intracellular
C-terminal domains which are more diverse in
length and function across receptor sub-types.
GPCR-mediated
signaling is carried out by coupling of
heterotrimeric G proteins to the agonist-bound
receptor. Upon receptor activation the GTP-hydrolyzing
alpha subunit and beta/gamma dimer dissociate
from each other to form two independent
signaling units that signal through GPCR-associated
effector molecules including adenylyl cyclases,
ion channels, and other enzymes. This complex
and versatile signaling system regulates
cAMP production, intracellular Ca2+
and K+ levels, and controls cellular
processes such as sensory perception, synaptic
transmission, hormone release, cell growth and
differentiation.
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