FIGURE 8.

Interaction between HSC20 and ISCU. A, two-dimensional ¹H,¹⁵N TROSY-HSQC spectra of U-¹⁵N-ISCU (left panel), U-¹⁵N-ISCU in the presence of equimolar unlabeled HSC20 and diluted by a factor of 2.25 (middle panel), overlay of the NMR spectra from the left and middle panels (right panel). B, expansions of the Trp-76 ¹H,¹⁵N peaks from the spectra in A. C, %S calculated from FMLR analysis of the intensities of the Trp-76 cross-peaks assigned S and D under the conditions indicated. D, ¹H,¹⁵N TROSY-HSQC spectra of U-¹⁵N-ISCU(N90A) (left panel), U-¹⁵N-ISCU(N90A) in the presence of 1 eq of unlabeled HSC20 and diluted by a factor of 2.25 (middle panel), overlay of the NMR spectra from the left panel and middle panels (right panel). E, expansions of the Trp-76 ¹H,¹⁵N peaks from the spectra in D. F, %S calculated from FMLR analysis of the intensities of Trp-76 cross-peaks assigned S and D under the conditions indicated. G, chemical shift perturbation of ISCU signals (Δδ_HN) upon the addition of 1.0 eq of HSC20 plotted as a function of ISCU residue number. Red triangles indicate residues whose NMR peaks were broadened beyond detection upon addition of HSC20. H, chemical shift perturbations (Δδ_HN) for residues of ISCU(N90A) upon the addition of 1 eq of HSC20. I, chemical shift perturbations of ISCU signals resulting from HSC20 binding mapped onto the structure of Zn²⁺ bound M. musculus ISCU (PDB code 1WFZ) (47). Residues with Δδ_HN > 0.04 ppm are colored blue; residues whose NMR peaks were broadened beyond detection are colored red. J, chemical shift perturbations of ISCU(N90A) resulting from HSC20 binding mapped on the structure of Zn²⁺ bound M. musculus ISCU with color coding as in I.