Table 1. List of class A GPCRs included in the study.
| Subgrp idx | # GPCRs in subgrp | GPCRs included in the subgroupsa | Natural ligand | Chemical class of natural ligandb | Notesc |
| 1 | 5 | CHRM1 (ACM1), CHRM2 (ACM2), CHRM3 (ACM3), CHRM4 (ACM4), CHRM5 (ACM5) | acetylcholine | small | |
| 2 | 5 | DRD1, DRD2, DRD3, DRD4, DRD5 | dopamine | small | |
| 3 | 5 | P2RY12 (P2Y12), P2RY13 (P2Y13), P2RY14 (P2Y14), GPR87, GPR171 (GP171) | nucleotides, lysophosphatidic acid (GPR87) | small | o, S |
| 4 | 7 | HTR1A (5HT1A), HTR1B (5HT1B), HTR1D (5HT1D), 5HT1F (HTR1F), HTR1E (5HT1E), HTR5A (5HT5A), HTR7 (5HT7R) | 5-hydroxytryptamine | small | |
| 5 | 5 | P2RY1, P2RY2, P2RY4, P2RY6, P2RY11 (P2Y11) | nucleotides | small | |
| 6 | 3 | MTNR1A (MTR1A), MTNR1B (MTR1B), GPR50 (MTR1L) | melatonin | small | o |
| 7 | 5 | ADRA1A (ADA1A), ADRA1B (ADA1B), ADRB1, ADRB2, ADRB3 | Adrenaline | small | |
| 8 | 3 | HTR2A (5HT2A), HTR2B (5HT2B), HTR2C (5HT2C) | 5-hydroxytryptamine | small | |
| 9 | 4 | HRH1, HRH2, HRH3, HRH4 | Histamine | small | |
| 10 | 3 | ADORA1 (AA1R), ADORA2A (AA2AR), ADORA2B (AA2BR) | Adenosine | small |
a
The receptors are indicated through their gene name. Uniprot name, when different from the gene name, and common synonyms are listed in parentheses. Orphan receptors are indicated in bold and indicated as ‘o’ in Notes.
b
Small indicates “small molecules” and refers to biogenic amines, nucleosides and nucleotides.
c
The symbol “o” indicates that the subgroup has one or more orphan GPCR.