Abstract
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].
In the periphery, the adrenergic system plays an important role in regulating the cardiovascular system [6]. Increased sympathetic discharge to the heart increases the rate and force of contraction mediated through beta-1 receptors. Circulating adrenaline also acts on cardiac tissue, and, in addition acts both on alpha-1 adrenoceptors in arterial smooth muscle, stimulating vasoconstriction, and on beta-2 adrenoceptors in vascular beds of skeletal muscle, stimulating vasodilation [6]. In the CNS, noradrenaline is thought to be involved in the regulation of mood, and various psycho- active drugs alter noradrenergic function. Numerous drugs exert their actions via adrenoceptors: e.g., beta-2 selective agonists such as salbutamol are used in the acute treatment of asthma, while alpha agonists prolong the action of local anaesthetics, and act as nasal decongestants [6].
Adrenoceptors can be divided into three main classes based on sequence similarity, receptor pharmacology and signalling mechanisms. Further subdivisions exist within each class [6]. A large number of agonists and antagonists distinguish between the different classes of adrenoceptor; by contrast, relatively small differences in agonist and antagonist affinities are demonstrated, especially within the alpha-1 and alpha-2 adrenoceptor subtypes [6].
The alpha-1A receptor has not been detected in rat or bovine tissues by Northern analysis [6]. Its expression is thus either very low, or highly specialised in tissue distribution [6]. The receptor is coupled to the phosphoinositide pathway through a pertussis-toxin-insensitive G protein, probably of the Gq/G11 class [6].
ADRENRGCA1AR is a 6-element fingerprint that provides a signature for the alpha-1A adrenergic receptors. The fingerprint was derived from an initial alignment of 8 sequences: the motifs were drawn from conserved sections within either loop or N- and C-terminal regions, focusing on those areas of the alignment that characterise the alpha-1A adrenergic receptors but distinguish them from the rest of the rhodopsin-like superfamily - motif 1 lies at the N-terminus; motifs 2 and 3 lie in the third cytoplasmic loop; and motifs 4-6 span the C-terminus. A single iteration on OWL28.1 was required to reach convergence, no further sequences being identified beyond the starting set. A single partial match was also found, an alpha-1C receptor fragment that matches motifs 2 and 3.
An update on SPTR37_9f identified a true set of 8 sequences.
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.
Adrenaline and noradrenaline.
IN THE G PROTEIN-LINKED RECEPTOR FACTSBOOK, ACADEMIC PRESS, 1994, PP.32-54.
Sequence Matches
A1AA_HUMAN ALPHA-1A ADRENERGIC RECEPTOR (ALPHA 1A-ADRENOCEPTOR) (ALPHA-1C ADRENERGIC RECEPTOR) - HOMO SAPIENS (HUMAN).
Q13729 ALPHA 1C ADRENERGIC RECEPTOR ISOFORM 3 - HOMO SAPIENS (HUMAN).
Q13675 ALPHA 1C ADRENERGIC RECEPTOR ISOFORM 2 - HOMO SAPIENS (HUMAN).
O60451 ALPHA 1A ADRENERGIC RECEPTOR ISOFORM 4 - HOMO SAPIENS (HUMAN).
A1AA_RABIT ALPHA-1A ADRENERGIC RECEPTOR (ALPHA 1A-ADRENOCEPTOR) (ALPHA-1C ADRENERGIC RECEPTOR) - ORYCTOLAGUS CUNICULUS (RABBIT).
A1AA_RAT ALPHA-1A ADRENERGIC RECEPTOR (ALPHA 1A-ADRENOCEPTOR) (ALPHA-1C ADRENERGIC RECEPTOR) - RATTUS NORVEGICUS (RAT).
O54913 ALPHA 1A-ADRENERGIC RECEPTOR - MUS MUSCULUS (MOUSE).
A1AA_BOVIN ALPHA-1A ADRENERGIC RECEPTOR (ALPHA 1A-ADRENOCEPTOR) (ALPHA-1C ADRENERGIC RECEPTOR) - BOS TAURUS (BOVINE).
Composite Fingerprint Index
cd; 6| 8 8 8 8 8 8
cd; 5| 0 0 0 0 0 0
cd; 4| 0 0 0 0 0 0
cd; 3| 0 0 0 0 0 0
cd; 2| 0 0 0 0 0 0
cd; --+-------------------------------
cd; | 1 2 3 4 5 6
Final Motif Sets
A1A adrenergic receptor motif I - 2
Motif length 23
FLSGNASDSSNCTQPPAPVNISK A1AA_HUMAN 3 3
FLSGNASDSSNCTQPPAPVNISK Q13729 3 3
FLSGNASDSSNCTQPPAPVNISK Q13675 3 3
FLSGNASDSSNCTQPPAPVNISK O60451 3 3
FLSGNASDSSNCTHPPAPVNISK A1AA_RABIT 3 3
LLSENASEGSNCTHPPAPVNISK A1AA_RAT 3 3
LLSENASEGSNCTHPPAQVNISK O54913 3 3
FLSGNASDSSNCTHPPPPVNISK A1AA_BOVIN 3 3
A1A adrenergic receptor motif II - 2
Motif length 16
KSGLKTDKSDSEQVTL A1AA_HUMAN 219 193
KSGLKTDKSDSEQVTL Q13729 219 193
KSGLKTDKSDSEQVTL Q13675 219 193
KSGLKTDKSDSEQVTL O60451 219 193
KSGLKTDKSDSEQVTL A1AA_RABIT 219 193
KSGLKTDKSDSEQVTL A1AA_RAT 219 193
KSGLKTDKSDSEQVTL O54913 219 193
KSGLKTDKSDSEQVTL A1AA_BOVIN 219 193
A1A adrenergic receptor motif III - 2
Motif length 18
RKNAPAGGSGMASAKTKT A1AA_HUMAN 238 3
RKNAPAGGSGMASAKTKT Q13729 238 3
RKNAPAGGSGMASAKTKT Q13675 238 3
RKNAPAGGSGMASAKTKT O60451 238 3
RKNAPAGGSGVASAKNKT A1AA_RABIT 238 3
RKNVPAEGGGVSSAKNKT A1AA_RAT 238 3
RKNVPAEGSGVSSAKNKT O54913 238 3
RKNAQVGGSGVTSAKNKT A1AA_BOVIN 238 3
A1A adrenergic receptor motif IV - 2
Motif length 18
LGYTLHPPSQAVEGQHKD A1AA_HUMAN 356 100
LGYTLHPPSQAVEGQHKD Q13729 356 100
LGYTLHPPSQAVEGQHKD Q13675 356 100
LGYTLHPPSQAVEGQHKD O60451 356 100
LGYTLHAPSQALEGQHKD A1AA_RABIT 356 100
LGYTLHPPSQALEGQHRD A1AA_RAT 356 100
LGYTLHPPSQAVEEQHRG O54913 356 100
LGYTLHAPSHVLEGQHKD A1AA_BOVIN 356 100
A1A adrenergic receptor motif V - 2
Motif length 20
RIPVGSRETFYRISKTDGVC A1AA_HUMAN 376 2
RIPVGSRETFYRISKTDGVC Q13729 376 2
RIPVGSRETFYRISKTDGVC Q13675 376 2
RIPVGSRETFYRISKTDGVC O60451 376 2
RIPVGSGETFYKISKTDGVC A1AA_RABIT 376 2
RIPVGSGETFYKISKTDGVC A1AA_RAT 376 2
RIPVGSGETFYKISKTDGVC O54913 376 2
RIPVGSAETFYKISKTDGVC A1AA_BOVIN 376 2
A1A adrenergic receptor motif VI - 2
Motif length 20
FSSMPRGSARITVSKDQSSC A1AA_HUMAN 400 4
FSSMPRGSARITVSKDQSSC Q13729 400 4
FSSMPRGSARITVSKDQSSC Q13675 400 4
FSSMPRGSARITVSKDQSSC O60451 400 4
FSSMPRGSARITVPKDQSAC A1AA_RABIT 400 4
FSSMPQGSARITVPKDQSAC A1AA_RAT 400 4
FSSMPQGSARITMPKDQSAC O54913 400 4
FSSLPRGSARMAVARDPSAC A1AA_BOVIN 400 4