Table 2.
smFRET conformational states occupied by AMPA receptor
ConstructStateOccupancy (%)StaSI efficiency stateFRET distance (Å)Gaussian stateCα–Cα structure distance (Å)
(Protein Data Bank accession no.)
AMPA receptor (D23C) apo State 1 94.55 0.88 37 ± 0.5 0.88 ± 0.01 35 
(4U2Pa) 
State 2 5.45 0.55 50 ± 0.7 0.53 ± 0.02 41 
(5L1Ba) 
AMPA receptor (D23C)/γ8 apo State 1 87.72 0.89 34 ± 0.8 0.92 ± 0.01  
State 2 12.28 0.61 46 ± 0.7 0.64 ± 0.02 
AMPA receptor (D23C) Glu + CTZb State 1 69.18 0.89 35 ± 0.7 0.90 ± 0.01 41 
(4UQKc) 
43 
State 2 30.82 0.76 42 ± 0.8 0.76 ± 0.02 (6DLZc) 
44 
(5WEOc) 
AMPA receptor (D23C) Glub State 1 17.0 0.90 34 ± 2.3 0.92 ± 0.03 33 
State 2 35.8 0.75 42 ± 0.4 0.76 ± 0.01 (4U1Yd) 
State 3 44.4 0.60 48 ± 0.3 0.60 ± 0.01 41 
State 4 2.1 0.44 52 ± 0.7 0.46 ± 0.02 (5VHZd) 
AMPA receptor (D23C)/γ8 Glu State 1 54.95 0.91 32 ± 1.0 0.94 ± 0.01  
State 2 45.05 0.70 42 ± 1.1 0.76 ± 0.03 
AMPA receptor (L467C) apo State 1 74.41 0.90 34 ± 0.8 0.92 ± 0.01 33 
(4U2Pa) 
State 2 25.59 0.68 45 ± 0.7 0.68 ± 0.02 33 
(5L1Ba) 
AMPA receptor (L467C)/γ8 apo State 1 65.74 0.92 34 ± 0.8 0.92 ± 0.01  
State 2 34.26 0.72 44 ± 0.7 0.72 ± 0.02 
AMPA receptor (L467C) Glu + CTZ State 1 40.60 0.94 31 ± 2.1 0.95 ± 0.02 33 
(4UQKc) 
State 2 17.91 0.87 38 ± 1.0 0.86 ± 0.02 34 
(6DLZc) 
State 3 24.34 0.77 42 ± 1.9 0.75 ± 0.05 34 
State 4 17.15 0.61 47 ± 0.3 0.61 ± 0.1 (5WEOc) 
AMPA receptor (L467C)/γ8 Glu State 1 35.89 0.94 30 ± 2.6 0.96 ± 0.02  
State 2 29.68 0.83 39 ± 2.4 0.84 ± 0.05 
State 3 17.34 0.70 44 ± 2.5 0.70 ± 0.07 
State 4 17.09 0.55 50 ± 1.3 0.52 ± 0.04 
AMPA receptor (L467C) Glu State 1 27.32 0.89 35 ± 1.4 0.91 ± 0.02 33 
State 2 52.32 0.76 42 ± 0.8 0.77 ± 0.02 (4U1Yd) 
State 3 16.64 0.60 48 ± 3.3 0.58 ± 0.1 40 
State 4 3.72 0.46 53 ± 3.6 0.42 ± 0.1 (5VHZd) 
ConstructStateOccupancy (%)StaSI efficiency stateFRET distance (Å)Gaussian stateCα–Cα structure distance (Å)
(Protein Data Bank accession no.)
AMPA receptor (D23C) apo State 1 94.55 0.88 37 ± 0.5 0.88 ± 0.01 35 
(4U2Pa) 
State 2 5.45 0.55 50 ± 0.7 0.53 ± 0.02 41 
(5L1Ba) 
AMPA receptor (D23C)/γ8 apo State 1 87.72 0.89 34 ± 0.8 0.92 ± 0.01  
State 2 12.28 0.61 46 ± 0.7 0.64 ± 0.02 
AMPA receptor (D23C) Glu + CTZb State 1 69.18 0.89 35 ± 0.7 0.90 ± 0.01 41 
(4UQKc) 
43 
State 2 30.82 0.76 42 ± 0.8 0.76 ± 0.02 (6DLZc) 
44 
(5WEOc) 
AMPA receptor (D23C) Glub State 1 17.0 0.90 34 ± 2.3 0.92 ± 0.03 33 
State 2 35.8 0.75 42 ± 0.4 0.76 ± 0.01 (4U1Yd) 
State 3 44.4 0.60 48 ± 0.3 0.60 ± 0.01 41 
State 4 2.1 0.44 52 ± 0.7 0.46 ± 0.02 (5VHZd) 
AMPA receptor (D23C)/γ8 Glu State 1 54.95 0.91 32 ± 1.0 0.94 ± 0.01  
State 2 45.05 0.70 42 ± 1.1 0.76 ± 0.03 
AMPA receptor (L467C) apo State 1 74.41 0.90 34 ± 0.8 0.92 ± 0.01 33 
(4U2Pa) 
State 2 25.59 0.68 45 ± 0.7 0.68 ± 0.02 33 
(5L1Ba) 
AMPA receptor (L467C)/γ8 apo State 1 65.74 0.92 34 ± 0.8 0.92 ± 0.01  
State 2 34.26 0.72 44 ± 0.7 0.72 ± 0.02 
AMPA receptor (L467C) Glu + CTZ State 1 40.60 0.94 31 ± 2.1 0.95 ± 0.02 33 
(4UQKc) 
State 2 17.91 0.87 38 ± 1.0 0.86 ± 0.02 34 
(6DLZc) 
State 3 24.34 0.77 42 ± 1.9 0.75 ± 0.05 34 
State 4 17.15 0.61 47 ± 0.3 0.61 ± 0.1 (5WEOc) 
AMPA receptor (L467C)/γ8 Glu State 1 35.89 0.94 30 ± 2.6 0.96 ± 0.02  
State 2 29.68 0.83 39 ± 2.4 0.84 ± 0.05 
State 3 17.34 0.70 44 ± 2.5 0.70 ± 0.07 
State 4 17.09 0.55 50 ± 1.3 0.52 ± 0.04 
AMPA receptor (L467C) Glu State 1 27.32 0.89 35 ± 1.4 0.91 ± 0.02 33 
State 2 52.32 0.76 42 ± 0.8 0.77 ± 0.02 (4U1Yd) 
State 3 16.64 0.60 48 ± 3.3 0.58 ± 0.1 40 
State 4 3.72 0.46 53 ± 3.6 0.42 ± 0.1 (5VHZd) 

STaSI, step transition and state identification used to determine the states as stated in Materials and methods. Gaussian states were obtained from fitting the observed data.

a

Structures 4U2P and 5L1B represent the apo structure of the receptor.

b

Data from Shaikh et al. (2016).

c

Structures 4UQK, 6DLZ, and 5WEO represent the open structure of the receptor.

d

Structures 4U1Y and 5VHZ represent the desensitized structure of the receptor.

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