Table 1. Summary of the human GPCR set.

Group	Sub-family	Description	Pro in TM2	TM2 Pro position	Pro in TM5	WXFG motif
G0	PEP	Peptide receptors	+++	2.59	+++	++
	OPN	Opsins	++	2.59	+++	+++
	MTN	Melatonin receptors	+++	2.59	+++	++
G1	SO	Somatostatin/opioid receptors	+++	2.58	+++	+++
	CHEM	Chemotactic receptors	+++	2.58	+++	+++
	PUR	Purinergic receptors	+++	2.58	+++	++
G2	AMIN	Amine receptors	+++	2.59	+++	++
	AD	Adenosine receptors	+++	2.59	+++	–
G3	LGR	Leucine-rich repeat receptors	–	–	–	Δ
	MEC	Melanocortin, S1P and cannabinoid receptors	–	–	–	–
	PTG	Prostaglandin receptors	++	2.59	–	+
	MRG	MAS-related receptors	–	–	+	–

Human non-olfactory class A GPCRs were assigned to twelve sub-families according to the detailed classification reported in [6], except for the split of the MECA receptors into the AD and MEC sub-families. 7% of the human receptors could not be classified. The symbols indicate the percent of sequences with the pattern considered in human GPCRs (–, +, ++ and +++ correspond to 0%, 0 to 50%, 50 to 80% and ≥80%, respectively). Proline was searched for from position 2.58 to 2.60 in TM2 and at position 5.50 in TM5. The main proline position in TM2 is italic, normal and bold when it is observed in < 50%, 50 to 80% and ≥ 80% of the sequences. Δ indicates that the WXFG motif is shifted to positions 3.19–3.22.