Supplemental Table 1. Crystallographic statistics
Data collection
FcRI
(I41)
Dataset
Native
Native
Unit cell
dimensions (Å)
a=158.6
b=158.6
c=39.9
a=88.0
b=91.7
c=171.4
a=142.5
b=142.5
c=67.5
Wavelength (Å)
1.00
0.949
0.951
1.362
0.97
1.00
0.95
3.0
(3.05-3.00)
3.15
(3.20-3.15)
3.15
(3.20-3.15)
3.15
(3.20-3.15)
3.45
(3.51-3.45)
3.9
(3.97-3.90)
3.1
(3.21-3.10)
Observations
154,491
83,520
52,434
51,631
37,381
50,469
213,861
Unique reflections
10,246
8,904
8,945
8,913
5,778
6,628
27,807
7.7 (40.4)
10.6 (37.2)
10.6 (40.6)
9.1 (35.2)
12.5 (43.5)
17.7 (41.7)
8.9 (31.0)
Completeness (%)*
99.7 (100)
99.1 (92.4)
98.7 (87.9)
98.4 (84.9)
99.9 (99.6)
84.1 (63.8)
95.8 (71.6)
I/I*
22.4 (4.9)
12.8 (2.5)
10.2 (2.1)
12.6 (2.6)
9.4 (2.7)
5.4 (2.5)
12.0 (2.4)
FcRI
form I
FcRI:Fc
complex
FcRI
form I
FcRI:Fc
complex
Resolution
25-3.0
30-3.1
rmsd bond lengths (Å)
0.008
0.009
No. of reflections
(working set) |F|>0
8,599
25,384
rmsd bond angles (°)
1.43
1.52
No. of reflections
(test set) |F|>0
991
1,300
rmsd dihedrals (°)
26.5
26.5
rmsd impropers (°)
1.08
1.29
Resolution
Rmerge
(%)*†
Pb inflection
Pb remote
U
Complex
(P3)
Native
(Å)*
Pb peak
FcRI
(I212121)
Refinement
No. of nonhydrogen atoms
Total
2,886
6,284
Protein
2,808
5,702
Ramachandran plot
Carbohydrate
70
582
Favored (%)
78.1
75.7
Other
8
Allowed (%)
19.7
22.1
Rcryst (%)‡
23.5
25.1
Generous (%)
2.2
2.2
(%)‡
29.1
28.4
Disallowed (%)
0.0
0.0
Rfree
*
Last shell is shown in parentheses.
†
Rmerge (I) = (∑|I(i) - <I>| / ∑I(i)), where I(i) is the ith observation of the intensity of a particular
reflection and <I> is the average intensity of that reflection.
‡
Rcryst (F) = ∑||Fobs| - |Fcalc|| / ∑|Fobs|, where Fobs and Fcalc are the observed and calculated structure
factor amplitudes, respectively. Rfree was calculated for a test set containing randomly chosen
reflections that were not included in the refinement.
Supplemental Table 2. RMS deviations between FcRI or Fc and related
proteins
FcRI
D1
D2
Fc
C2
C3
LIR-11
rmsd (Å)
1.73 (69)a
1.57 (78)
KIR2
rmsd (Å)
1.74 (72)
1.23 (87)
FcRIIa3
rmsd (Å)
1.53 (64)
1.33 (66)
Fc7
rmsd (Å)
1.42 (88)
0.94 (100)
Fc3-48
rmsd (Å)
1.38 (84)
1.15 (90)
Fc2-49
rmsd (Å)
1.45 (89)
1.18 (92)
FcRIIb4
rmsd (Å)
1.73 (64)
1.28 (66)
FcRIII5
rmsd (Å)
1.44 (62)
1.31 (72)
FcRI6
rmsd (Å)
1.72 (64)
1.46 (79)
Rms deviations between domains were calculated using LSQMAN 10.
a
Values in parentheses are the number of C atoms used in the calculation.
Supplemental Table 3. Pairwise interactions in the FcRI:Fc interfacea
FcRI
residue
Tyr-35
% ASA
(Å2)
7
Arg-52
Arg-53
Leu-54
6
3
16
Lys-55
9
Phe-56
10
Mutation (effect on affinity)b
Y35A, 100x 
R52A, 8x 
R53A, no effect
Trp-57
Arg-82
3
5
R82A, ablation; R82G, ablationd
Gly-84
5
G84A, 19x 
His-85
16
H85A, 4x ; H85E, ablationd
Man-923
(Asn-58)
Man-927
(Asn-58)
a
4
10
Fc
residue
Leu-257
Leu-258
Phe-443
Leu-258
Ser-387
Leu-258
Arg-382
Leu-384
Glu-389
Met-433
Ser-387
Met-433
Gln-445
Met-433
Leu-441
Phe-443
Gln-445
Ser-387
Leu-256
Leu-257
Pro-440
Leu-441
% ASA
(Å2)
8
10
5
Mutation (effect on binding)c
L257R, ablation
L258R, ablatione
F443R, ablation
L258R, ablation
10
L258R, ablatione
1
3
5
6
6
12
LA441-442MN, ablation;
L441R, ablatione
F443R, ablation
3
8
Ala-442
Leu-257
His-436
Glu-437
Ala-438
Leu-439
Ala-442
Pro-440
4
Glu-348
Thr-444
7
3
L257R, ablation
P440A, ablation; P440R, 10x 
LA441-442MN, ablation;
L441R, ablatione
A442R, ablation
L257R, ablation
1
2
0
1
A442R, ablation
P440A, ablation; P440R, 10x 
Pairwise interactions in the FcRI:Fc interface between any nonhydrogen atoms within 4 Å were
determined using CNS11.
b From 12;
affinities determined by biosensor binding studies, except where noted.
c From 13;
binding determined by rosetting assay, except where noted. d From14; affinities determined
by gel shift assay
e From 15;
binding determined by rosetting assay.
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