| Literature References | 1. ATTWOOD, T.K. AND FINDLAY, J.B.C.
Fingerprinting G protein-coupled receptors.
PROTEIN ENG. 7(2) 195-203 (1994).
2. ATTWOOD, T.K. AND FINDLAY, J.B.C.
G protein-coupled receptor fingerprints.
7TM, VOLUME 2, EDS. G.VRIEND AND B.BYWATER (1993).
3. BIRNBAUMER, L.
G proteins in signal transduction.
ANNU.REV.PHARMACOL.TOXICOL. 30 675-705 (1990).
4. CASEY, P.J. AND GILMAN, A.G.
G protein involvement in receptor-effector coupling.
J.BIOL.CHEM. 263(6) 2577-2580 (1988).
5. ATTWOOD, T.K. AND FINDLAY, J.B.C.
Design of a discriminating fingerprint for G protein-coupled receptors.
PROTEIN ENG. 6(2) 167-176 (1993).
6. WATSON, S. AND ARKINSTALL, S.
Melanocortins.
IN THE G PROTEIN-LINKED RECEPTOR FACTSBOOK, ACADEMIC PRESS, 1994, PP.180-191.
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| Documentation | G protein-coupled receptors (GPCRs) constitute a vast protein family that
encompasses a wide range of functions (including various autocrine, para-
crine and endocrine processes). They show considerable diversity at the
sequence level, on the basis of which they can be separated into distinct
groups. We use the term clan to describe the GPCRs, as they embrace a group
of families for which there are indications of evolutionary relationship,
but between which there is no statistically significant similarity in
sequence [1]. The currently known clan members include the rhodopsin-like
GPCRs, the secretin-like GPCRs, the cAMP receptors, the fungal mating
pheromone receptors, and the metabotropic glutamate receptor family.
The rhodopsin-like GPCRs themselves represent a widespread protein family
that includes hormone, neurotransmitter and light receptors, all of
which transduce extracellular signals through interaction with guanine
nucleotide-binding (G) proteins. Although their activating ligands vary
widely in structure and character, the amino acid sequences of the
receptors are very similar and are believed to adopt a common structural
framework comprising 7 transmembrane (TM) helices [3-5].
Adrenocorticotrophin (ACTH), melanocyte-stimulating hormones (MSH) and
beta-endorphin are peptide products of pituitary pro-opiomelanocortin.
ACTH regulates synthesis and release of glucocorticoids and aldosterone
in the adrenal cortex; it also has a trophic action on these cells [6].
ACTH and beta-endorphin are synthesised and released in response to
corticotrophin-releasing factor at times of stress (heat, cold, infections,
etc.) - their release leads to increased metabolism and analgesia res..
MSH has a trophic action on melanocytes, and regulates pigment production
in fish and amphibia [6]. The ACTH receptor is found in high levels in
the adrenal cortex - binding sites are present in lower levels in the
CNS. The MSH receptor is expressed in high levels in melanocytes,
melanomas and their derived cell lines [6]. Receptors are found in low
levels in the CNS. MSH regulates temperature control in the septal region
of the brain and releases prolactin from the pituitary.
MCRFAMILY is a 7-element fingerprint that provides a signature for the
melanocortin receptors. The fingerprint was derived from an initial
alignment of 6 sequences: the motifs were drawn from conserved sections
within either loop or TM regions, focusing on those areas of the
alignment that characterise the melanocortin receptors but distinguish them
from the rest of the rhodopsin-like superfamily - motif 1 spans the first
cytoplasmic loop; motif 2 spans part of the first external loop leading
into TM domain 3; motif 3 lies in the second cytoplasmic loop; motif 4
encodes the N-terminus of TM domain 6; motif 5 lies in the third external
loop; motif 6 was drawn from the N-terminus of TM domain 7; and motif 7
resides in the C-terminal region following TM domain 7. Two iterations on
OWL27.1 were required to reach convergence, at which point a true set
comprising 20 sequences was identfied. Several partial matches were also
found: those matching 4 or 5 motifs are largely melanocortin receptor
fragments; while those matching just 2 motifs are members of the wider
rhodopsin-like superfamily.
An update on SPTR37_9f identified a true set of 32 sequences.
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