FIGURE 3.

Backbone chemical shift assignment of the PFUC domain showing cis/trans isomerization and Ub binding. A, ¹H-¹⁵N HSQC spectrum of PFUC with assigned resonance peaks. The peaks in rectangles indicate the duplicate signals that originate from cis/trans-isomerization of proline residues. B, diagram of the chemical shift changes (Δδ) of PFUC against its residue number at a PFUC/Ub molar ratio of 1:4. The changes in the cis-isomer are shown in red bars, and those in the trans form are in green. The two horizontal lines indicate mean Δδ and mean Δδ plus S.D. values. C, diagram of the chemical shift changes (Δδ) of Ub against its residue number. ¹⁵N-Labeled Ub was titrated with PFUC at a Ub/PFUC molar ratio of 1:4.