Table S1.

Statistics for 25 lowest-energy pUBL structures

Completeness of resonance assignments
Backbone (N, CA)	(147/149), 98.7%
Sidechain (C, H)	(663/679), 96.4%
HN	(71/73), 97.3%
HA	(79/79), 100.0%
HB	(122/122), 100.0%
NMR distance and dihedral constraints
Distance constraints
Total	1,014
Intraresidue	299
Interresidue
Sequential (i − j = 1)	258
Medium range ($1<|i-j|<5$)	152
Long range ($|i-j|>5$)	305
Intermolecular	0
Hydrogen bonds	52
Dihedral angle restraints (phi, psi)*	38
Structure statistics†
Violations (mean and SD)
Distance constraints, Ň	0
Dihedral angles constraints, $°$	$0.267\pm 0.154$
Maximum dihedral angle violation, $°$	1.82
Maximum distance constraint violation, Ň	0
Deviations from idealized geometry
Bond lengths, Å	$0.006\pm 0.000$
Bond angles, $°$	$0.582\pm 0.014$
Impropers, $°$	$0.740\pm 0.067$
Ramachandran statistics§
Most favored	85.1%
Additionally favored	14.2%
Generously favored	0.2%
Disallowed	0.6%
rmsd to mean structure, Ŷ
Heavy	$1.104\pm 0.123$
Backbone	$0.658\pm 0.110$

^*Talos-derived phi/psi angles.

^†As reported by X-PLOR-NIH, using all residues.

^‡No distance violation $>0.1$ Å.

^§As reported by Procheck, using all residues.

^¶rmsd to averaged coordinates using residues 1–71.