Table 1. M2-cap Sequence Alignment of Cys-loop receptors.

subunit	18′	19′	20′	21′	22′	23′	24′	25′	26′	27′	28′
AChR α1	I	V	E	L	I	P 265	S	T	S	S	A
AChR α2	I	T	E	I	I	P 276	S	T	S	L	V
AChR α3	I	T	E	T	I	P 269	S	T	S	L	V
AChR α4	I	T	E	I	I	P 279	S	T	S	L	V
AChR α5	I	T	E	T	I	P	S	T	S	L	V
AChR α6	I	T	E	T	I	P 274	S	T	S	L	V
AChR α7	V	A	E	I	M	P 264	A	T	S	D	S
AChR α9	V	A	E	I	M	P 102	A	S	E	N	V
AChR α10	L	A	E	S	M	P 270	P	A	E	S	V
AChR β1	L	A	D	K	V	P 276	E	T	S	L	A
AChR β2	I	S	K	I	V	P 265	P	T	S	L	D
AChR β3	I	E	E	I	I	P 270	S	S	S	K	V
AChR β4	I	S	K	I	V	P 262	P	T	S	L	D
AChR δ	I	S	K	R	L	P 279	A	T	S	M	A
AChR γ	V	A	K	K	V	P 274	E	T	S	O	A
AChR ε	I	A	Q	K	I	P 275	E	T	S	L	S
GABA α1	A	R	N	S	L	P 304	K	V	A	Y	A
GABA α2	A	R	N	S	L	P 305	K	V	A	Y	A
GABA α3	A	R	N	S	L	P 330	K	V	A	Y	A
GABA α4	A	R	H	S	L	P 337	K	V	S	Y	A
GABA α6	A	R	H	S	L	P 284	K	V	S	Y	A
GABA β1	L	R	E	T	L	P 298	K	I	P	Y	V
Gly α1	S	R	A	S	L	P 299	K	V	S	Y	V
Gly β	L	A	A	E	L	P 321	K	V	S	Y	V
5HT 3A	V	S	D	T	L	P 278	A	T	A	I	G
5HT 3B	M	S	D	E	V	P 289	R	S	A	G	C

The entire sequence for the AChR α1 subunit (IVELIPSTSSA) is conserved in all vertebrates. Position 23′ is a proline (bold) in all cys-loop receptors. The superscripts on the conserved Pro represent the residue number.