FIGURE 6.

Quantitative analysis of the Ub binding affinities of PFUC and its mutants. A, titration of ¹⁵N-labeled Ub with three PFU fragments, PFUC, PFU, and UIM-PFU. B, titration of ¹⁵N-labeled wild-type and P77A mutant of PFUC with unlabeled Ub. C, titration of ¹⁵N-labeled Ub with unlabeled PFUC mutants in α1-helix (L91A and L97A) and in α2-helix (M105A, D108N, and M105A/D108N). D, titration of ¹⁵N-labeled Ub with unlabeled PFUC mutants in the P77 loop region (D71N, V72F, and V72G). The average chemical shift changes of Leu⁷¹ in Ub are shown in A, C, and D, and those of Ala¹¹¹ in PFUC or the P77A mutant are shown in B.