Structure Ligand bound Conformational state PDB Resolution (Å) Reference
AChR None Closed (Resting) 2BG9 4.0 [19]
AChR ACh
ACh 		Closed (Desensitized)
Open 		4AQ5
4AQ9		 6.2
6.2 		[20]
α1 α-BTx Open 2QC1 1.94 [28]
α1-13-residue peptide α-BTx - 1HCB 1.8 [52]
Ls-AChBP HEPES Intermediate 1I9B 2.70 [21]
Ls-AChBP HEPES
(-)-Nicotine
CCh		 Intermediate
Closed
Closed		 1UX2
1UW6
1UV6		 2.2
2.2
2.5		 [53]
Ls-AChBP α-CbTx Open 1YI5 4.20 [54]
Ls-AChBP DHβE Closed 4ALX 2.51 [42]
hα7/Ls-AChBP chimera n-Acetyl-d-glucosamine
(+)-Epibatidine		 Apo
Closed		 3SQ9
3SQ6		 3.10
2.80		 [62]
Bt-AChBP CAPS Intermediate 2BJ0 2.0 [55]
Ac-AChBP None
(+)-Epibatidine
α-Lobeline
MLA
α-CTxImI		 Apo
Closed
Closed; g-to-t
Intermediate
Open		 2BYN
2BYQ
2BYS
2BYR
2BYP		 2.02
3.40
2.05
2.45
2.07 		[46]
Ac-AChBP HEPES
α-CTxPnIA(A10L/D14K)		 Intermediate
Open		 2BR7
2BR8		 3.0
2.4 		[56]
Ac-AChBP SPX
GYM		 Intermediate
Intermediate		 2WZY
2X00		 2.51
2.40		 [49]
Ac-AChBP α-CTxImI Open 2C9T 2.2 [57]
Ac-AChBP α-CTxTxIA(A10L) Open 2UZ6 2.4 [50]
Ac-AChBP Cocaine
Galantamine		 Unchanged
Unchanged		 2PGZ
2PH9		 1.76
2.88		 [43]
Ac-AChBP Imidacloprid
Thiacloprid		 Closed
Closed		 3C79
3C84		 2.48
1.94		 [58]
Ac-AChBP Clothianidin
Imidacloprid		 Closed
Closed		 2ZJV
2ZJU		 2.70
2.58		 [16]
Ac-AChBP Sulfate Coordinated with Lys residues 3GUA 3.10 [59]
Ac-AChBP Anabaseine
DMXBA
4OH-DMXBA
Tropisetron		 Closed
Intermediate
Intermediate
Intermediate		 2WNL
2WNJ
2WN9
2WNC		 2.70
1.80
1.75
2.20 		[45]
Ac-AChBP None
Compound 31
Compound 35		 Apo; g
Intermediate
Intermediate		 2Y7Y
2W8F
2W8G		 1.89
2.7
2.8 		[44]
Ac-AChBP Metocurine
d-TC 		-
-		 3PEO
3PMZ 		2.10
2.44		 [60]
Ac-AChBP Fragment 1
Compound 3
Compound 4
Compound 6		 Open; g
g-to-t
g-to-t
endo		 2Y54
2Y56
2Y57
2Y58		 3.65
3.59
3.30
3.25 		[39]
Ac-AChBP
(Y53C mutant)		 MTSET+
MMTS and ACh		 Open
Closed		 2XZ6
2XZ5		 3.14
2.80		 [51]
  Ac-AChBP   d-TC
Strychnine		   Open
Closed		   2XYT
2XYS		   2.05
1.91		   [40]
hα7/Ac-AChBP chimera Mutant I
Mutant II + MLA
Mutant III + MLA		 Apo
-
- 		3T4M
3SH1
3SIO		 3.00
2.90
2.32		 [61]
Ac-AChBP Compound 18 (complex I)
Compound 6 (complex II)
Compound 6(complex III) 		Open
Open
Open		 2XNT
2XNU
2XNV 		3.21
2.55
2.44		 [63]
Ac-AChBP Varenicline
Cytisine 		Closed
Closed 		4AFT
4AFO		 3.20
2.88 		[41]
Ac-AChBP Triazole 18 - 4DBM 2.30 [64]
Bg-AChBP1
Bg-AChBP2		 None
None		 Pentagonal dodecahedron 4AOD
4AOE		 ~6
~6		 [29]
Ct-AChBP None Apo - Low resolution [65]
Ct-AChBP Varenicline
α-Lobeline		 Intermediate; g-to-t
Closed; g-to-t		 4AFG
4AFH		 2.0
1.9		 [30]
Ct-AChBP Compound 5 Intermediate 4B5D 2.3 [66]
AChRs are obtained from Torpedo marmorata electric fish.
AChBPs are obtained from Lymnaeastagnalis(Ls), Aplysiacalifornica(Ac), Bulinustruncatus(Bt), Biomphalariaglabrata (Bg), and Capitellateleta(Ct), respectively.
The close (i.e., contracted) and opened (i.e., extended) states of Loop C in the AChBP-ligand complexes indicate the active/desensitized (i.e., agonists) and resting (i.e., antagonists) states, respectively. Several ligands, including partial agonists, adoptan intermediate configuration between that for full agonists and competitive antagonists, where as allosteric modulators (e.g., cocaine and galantamine) do not produce any apparent change on Loop C. The g-to-t (also called Tyr-flip) conformational state corresponds to the opening of the lobe line pocket. The g state is the closed lobeline pocket, whereas in the endoconfiguration the ligand is unable to induce the opening of the lobe line pocket.
Table 1: Conformation states of AChRs and AChBPsin unbound and bound conditions.