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A search of SwissPROT using CAR1_DICDI is shown below. This sequence seems to bridge the two G-protein coupled receptor families by showing signficant similarity with both the calcitonin/secretin family C/S and the rhodopsin family R.
The best scores are: s-w Z-score E(43470) CAR1_DICDI CYCLIC AMP RECEPTOR 1. 2678 3208.3 0 CAR3_DICDI CYCLIC AMP RECEPTOR 3. 1524 1819.9 0 CAR2_DICDI CYCLIC AMP RECEPTOR 2. 1497 1789.8 0 CALR_HUMAN CALCITONIN RECEPTOR PRECURSOR (CT-R). 167 189.4 0.00042 C/S IL8B_HUMAN HIGH AFFINITY INTERLEUKIN-8 RECEPTOR B 161 185.1 0.00073 R CLRA_RAT CALCITONIN RECEPTOR A PRECURSOR (CT-R-A) 162 183.6 0.00087 C/S CLRB_RAT CALCITONIN RECEPTOR B PRECURSOR (CT-R-B) 162 183.0 0.00095 C/S DIHR_MANSE DIURETIC HORMONE RECEPTOR (DH-R). 150 170.9 0.0045 C/S YOW3_CAEEL PROBABLE G PROTEIN-COUPLED RECEPTOR ZK6 151 169.7 0.0052 CALR_PIG CALCITONIN RECEPTOR PRECURSOR (CT-R). 145 163.2 0.012 C/S GLR_RAT GLUCAGON RECEPTOR PRECURSOR (GL-R). 145 163.1 0.012 C/S IL8B_RABIT HIGH AFFINITY INTERLEUKIN-8 RECEPTOR B 141 161.0 0.016 R RDC1_HUMAN G PROTEIN-COUPLED RECEPTOR RDC1 HOMOLOG 139 158.5 0.022 R G10D_RAT PROBABLE G PROTEIN-COUPLED RECEPTOR G10D 133 150.5 0.061 R >>CYB_CROLA CYTOCHROME B (EC 1.10.2.2). 132 149.6 0.069 << NY1R_XENLA NEUROPEPTIDE Y RECEPTOR TYPE 1 (NPY1-R) 131 148.7 0.077 R OPSD_HUMAN RHODOPSIN. 130 148.0 0.085 R VIPR_HUMAN VASOACTIVE INTESTINAL POLYPEPTIDE RECEP 131 146.8 0.098 C/S OPSD_SPHSP OPSIN. 129 146.1 0.11 R SCRC_RAT SECRETIN RECEPTOR PRECURSOR. 129 144.6 0.13 C/S IL8A_HUMAN HIGH AFFINITY INTERLEUKIN-8 RECEPTOR A 127 144.3 0.14 R GLPR_RAT GLUCAGON-LIKE PEPTIDE 1 RECEPTOR PRECURSO 128 143.1 0.16 C/S AG2S_XENLA TYPE-1-LIKE ANGIOTENSIN II RECEPTOR 2 ( 126 142.8 0.16 R >>CYB_MONDO CYTOCHROME B (EC 1.10.2.2). 126 142.4 0.17 << >>CYB_ANGRO CYTOCHROME B (EC 1.10.2.2) (FRAGMENT). 122 141.8 0.19 << AG2R_BOVIN TYPE-1 ANGIOTENSIN II RECEPTOR (AT1). 125 141.7 0.19 R >>CYB_CYPCA CYTOCHROME B (EC 1.10.2.2). 125 141.2 0.20 << OPSD_CANFA RHODOPSIN. 124 140.8 0.21 R >>CYB_XENLA CYTOCHROME B (EC 1.10.2.2). 122 137.6 0.32 << OPRM_RAT MU-TYPE OPIOID RECEPTOR (MOR-1) (OPIOID R 122 137.2 0.34 R >>GABP_ECOLI GABA PERMEASE (4-NH2 BUTYRATE TRANS) 123 137.0 0.35 << OPSD_CRIGR RHODOPSIN. 120 136.0 0.40 R OPRM_HUMAN MU-TYPE OPIOID RECEPTOR (MOR-1). 121 136.0 0.40 R AG2R_RABIT TYPE-1 ANGIOTENSIN II RECEPTOR (AT1). 120 135.7 0.41 R GRFR_HUMAN GROWTH HORMONE-RELEASING HORMONE RECEPT 121 135.5 0.42 C/S SSR1_HUMAN SOMATOSTATIN RECEPTOR TYPE 1 (SS1R) (SR 119 133.7 0.53 R VIPR_RAT VASOACTIVE INTESTINAL POLYPEPTIDE RECEPTO 120 133.5 0.54 C/S IL8B_RAT HIGH AFFINITY INTERLEUKIN-8 RECEPTOR B (I 118 133.4 0.55 R AA3R_RAT ADENOSINE A3 RECEPTOR (TGPCR1). 116 131.9 0.67 R TA2R_MOUSE THROMBOXANE A2 RECEPTOR (TXA2-R). 116 131.3 0.71 R GRFR_PIG GROWTH HORMONE-RELEASING HORMONE RECEPTOR 118 131.3 0.72 C/S TA2R_HUMAN THROMBOXANE A2 RECEPTOR (TXA2-R). 115 130.1 0.84 R OPSD_BOVIN RHODOPSIN. 115 130.0 0.85 R AG2R_HUMAN TYPE-1A ANGIOTENSIN II RECEPTOR (AT1A). 115 129.7 0.88 R CRFR_RAT CORTICOTROPIN RELEASING FACTOR RECEPTOR P 116 129.6 0.89 C/S SSR5_RAT SOMATOSTATIN RECEPTOR TYPE 5 (SOMATOSTATI 115 129.6 0.89 R GRFR_MOUSE GROWTH HORMONE-RELEASING HORMONE RECEPT 116 129.5 0.91 C/S >>CYB_PARLI CYTOCHROME B (EC 1.10.2.2). 115 129.2 0.94 <<
Note that in this example, there are several cytochrome B sequences (which are not members of the G-protein-coupled reseptor family) that obtain very high similarity scores. Thus, one might be suspicious of the conclusion, since unrelated sequences have expectation values << 1.0. The next table shows the results of searching SwissPROT using the SSEARCH program with very slightly higher gap penalties, -14/-2 instead of -12/-2.