Figure 5: Experimental validation of the models.
(a) Superposition of the hetero single quantum coherence spectra of 15N uniformly labelled CyaY (light blue) with the final point of a titration with unlabelled IscS (1:1 molar ratio, black). (b) Residues of CyaY (1SOY) involved in the interaction with IscS (blue) and IscU (red). (c) Superposition of the hetero single quantum coherence spectra of the CyaY/IscS complex (black) with the final point of titration with unlabelled IscU (up to 1:1:1 molar ratios, red). (d) Mapping of IscS mutations into the IscS/IscU crystal structure (3LVL). To highlight the symmetry relation, the backbone of one of the IscS protomers is shown in blue with the complexed IscU shown in red, whereas the backbones of the corresponding symmetry related to IscS/IscU are shown in grey. A linear fog effect was applied. The side chains of mutated residues, which have no effect on the interaction with CyaY, are shown in green, those that abolish interaction are shown in yellow. The dimer interface and the presence of IscU delimit a small cavity in which CyaY is accommodated. (e) Electrostatic surface of unbound IscS. An arrow indicates the position of the positively charged patch involved in binding. The patch comprises residues arginines 55, 67, 219–220, 223, 225 and 237. The residues 220, 223 and 225 are those that, if mutated to glutamates, abolish CyaY binding. IscS is oriented as in d and rotated by 90° around the horizontal x axis.
