Figure 1.

Interaction of SH3^MutΔ56 with apo GroEL. (A) Ribbon diagrams showing a superposition of the structures of SH3^MutΔ56 (blue) and SH3^WTΔ57 (green), representing mimetics of a folding intermediate of the Fyn SH3 domain, determined from backbone chemical shifts and residual dipolar couplings using CS-Rosetta⁹ (see the Supporting Information and Figures S2 and S3). (B) ¹⁵N ΔR₂ observed for 100 μM ¹⁵N-labeled SH3^MutΔ56 in the presence of 120 μM (in subunits) apo GroEL at 900 MHz (blue circles) and 600 MHz (red circles) and 10 °C. The dashed lines represent the best fits obtained by simultaneously fitting all relaxation data (ΔR₂, DEST, and relaxation dispersion) to the model shown in Figure 3. The ΔR₂ effect is essentially abolished when the GroEL cavity is blocked by acid-denatured Rubisco (green circles). The gray bar indicates the residues deleted in SH3^MutΔ56. The sequence (residues in red are sites of mutations) and secondary structure are shown above the panel; the 3¹⁰ helix and β5 (dashed outline) are unfolded in SH3^MutΔ56, but only β5 is unfolded in SH3^WTΔ57 (see panel A). Error bars are one standard deviation. (C) Cross section through apo GroEL (Protein Data Bank entry 3E76¹⁰) illustrating the two cavities with a SH3^MutΔ56 molecule (orange, space-filling model) confined in each cavity.