Table S1.

Data collection and refinement statistics

Dataset	A-PGS SeMet derivative	A-PGS native	L-PGS
Temperature, K	100	100	100
Wavelength, Å	0.9797	0.9184	1.0332
Δϕ, °	0.7	0.5	0.2
Space group	P4122	P4122	P1
Unit cell parameters	a = 94.0 Å	a = 94.0 Å	a = 46.9 Å
	b = 94.0 Å	b = 94.0 Å	b = 66.3 Å
	c = 166.5 Å	c = 166.5 Å	c = 71.2 Å
	α = γ = 90°	α = γ = 90°	α = 112.4°
	β = 90°	β = 90°	β = 94.1°
	γ = 90°	γ = 90°	γ = 98.9°
Resolution range dmax-dmin, Å	50.0–3.1 (3.2–3.1)	20.0–2.3 (2.4–2.3)	40–2.1 (2.2–2.1)
No. of observed reflections	315,054 (23,659)	262,982 (26,038)	128,799 (2,501)
Completeness	0.999 (0.999)	0.995 (0.991)	0.806 (0.191)
Multiplicity	12.3 (12.2)	7.8 (7.9)	3.5 (3.5)
Rmerge*	0.307 (1.557)	0.159 (1.343)	0.095 (0.596)
Average I/σ,I	12.9 (2.1)	12.3 (2.0)	8.7 (2.0)
CC(1/2)†	0.994 (0.853)	0.997 (0.729)	0.994 (0.720)
Effective dmin‡, Å	3.1	2.4	2.4
Wilson B, Å2	56.1	37.4	27.5
Solvent content	0.74	0.74	0.52
Refinement
Rwork§	0.182	0.175	0.197
Rfree¶	0.213	0.199	0.248
No. of nonhydrogen atoms per asymmetric unit
Total	2,598	2,728	5,468
Protein	2,585	2,557	5,234
No. of molecules per asymmetric unit
Protein	1	1	2
Water	—	111	192
Ligands	5	16	3
Atomic displacement factors B, Å2
Overall	50.6	48.7	36.0
Protein	50.4	48.4	36.0
Water	—	46.2	34.4
Ligands	99.8	69.4	36.5
Rmsd from ideal
Bond lengths, Å	0.002	0.008	0.002
Bond angles, °	0.64	1.11	0.54
Ramachandran plot
Favored, %	96.3	95.6	95.7
Allowed, %	2.5	3.8	3.0

Values in parentheses are for the highest-resolution shell.

^*R_merge = Σ_hkl,i(Σ_i|I_hkl,i-〈I_hkl〉|/Σ_hkl,i〈I_hkl〉.

^†Fraction of correlation between intensities from random half-datasets (48).

^‡Resolution beyond which data completeness falls below the arbitrary threshold of 0.9 or the I/σ(I) average falls below 2.

^§R_work = (Σ||F_o|-|F_c||/Σ|F_o|); |F_o|, structure factor magnitudes observed; |F_c|, structure factors calculated.

^¶R_free is computed as R_work but using 5% randomly assigned reflections excluded from refinement.