G-protein coupled receptors [1,2,3,4] (also called R7G) are an extensive
group of hormones, neurotransmitters, odorants and light receptors which
transduce extracellular signals by interaction with guanine nucleotide-binding (G) proteins. The receptors that are currently known to belong to this
family are listed below.
5-hydroxytryptamine (serotonin) 1A to 1F, 2A to 2C, 4, 5A, 5B, 6 and 7 .
A number of orphan receptors (whose ligand is not known) from mammals and
Caenorhabditis elegans putative receptors C06G4.5, C38C10.1, C43C3.2,
T27D1.3 and ZC84.4.
Three putative receptors encoded in the genome of cytomegalovirus: US27,
US28, and UL33.
ECRF3, a putative receptor encoded in the genome of herpesvirus saimiri.
The structure of all these receptors is thought to be identical. They have
seven hydrophobic regions, each of which most probably spans the membrane.
The N-terminus is located on the extracellular side of the membrane and is
often glycosylated, while the C-terminus is cytoplasmic and generally
phosphorylated. Three extracellular loops alternate with three intracellular
loops to link the seven transmembrane regions. Most, but not all of these
receptors, lack a signal peptide. The most conserved parts of these proteins
are the transmembrane regions and the first two cytoplasmic loops. A conserved
acidic-Arg-aromatic triplet is present in the N-terminal extremity of the
second cytoplasmic loop  and could be implicated in the interaction with G
To detect this widespread family of proteins we have developed a pattern that
contains the conserved triplet and that also spans the major part of the third
transmembrane helix. We have also developed a profile that spans the seven
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