  Sci. STKE, 31 January 2006 Vol. 2006, Issue 320, p. tw43 [DOI:
10.1126/stke.3202006tw43]   G PROTEIN-COUPLED RECEPTORS
Different Conformations Prefer Distinct Signaling Pathways  The
metabotropic glutamate receptor 1α (mGluR1α), a homodimeric G
protein-coupled receptor critically involved in some forms of
synaptic plasticity, can stimulate an increase in intracellular
calcium concentration ([Ca2+]i) through Gq or an increase in
intracellular adenosine 3',5'-monophosphate (cAMP) concentration
([cAMP]i) through Gs. Each mGluR1α subunit contains an
extracellular "Venus flytrap" module; glutamate binding
stabilizes an active conformation in which the Venus flytrap of
one subunit closes while the other stays open (closed-
open/active, CO/A). In the presence of Gd3+, which binds to the
interface between subunits, glutamate binds to both subunits,
leading to a closed-closed/active (CC/A) conformation. Tateyama
and Kubo used fluorescent indicators to simultaneously measure
[Ca2+]i and [cAMP]i in CHO (Chinese hamster