Fig. 2: High resolution crystal structures of (NIAU2)2 complexes reveal flexibility of the ISCU2 N terminus.
From: N-terminal tyrosine of ISCU2 triggers [2Fe-2S] cluster synthesis by ISCU2 dimerization
a Overall architecture of the (NIAU2)2 complex obtained by X-ray crystallography. NFS1 subunits are depicted in orange and yellow, ISD11 in purple and magenta, ACP in dark and light green, and ISCU2 in dark and light blue. Each NFS1 subunit covalently binds a pyridoxal phosphate (PLP), and ACP carries a fatty acyl phosphopantetheinyl (FA-PPA) moiety. b Detailed view of the 6° tilting of ISCU2 in (NIAU2)2 relative to ISCU1 in (NIAU1)228. The conserved N-terminal Tyr35 of ISCU2 shows a dual localization within the crystal (inset). In one conformation (1*) Tyr35 stacks to Trp97 of NFS1’, and in the other (2*) it contacts Glu364 of NFS1. c Effect of exchanges of Tyr35 and His36 of ISCU2 on the mobility of the N terminus (for detailed crystallographic statistics refer to Supplementary Table 2). Residues 34-39 of ISCU2 (mutants) are shown by sticks, and water molecules were omitted. The electron density ‘omit’ map 2Fo-DFc is displayed at 0.8 sigma level near the N terminus of ISCU2. The map was calculated after removing residues 34–38 from the model and refining the model for one cycle with Phenix software. For stereo views refer to Supplementary Fig. 5c. Left: The mutant protein ISCU2-L35 shows a well-ordered N terminus with well-defined electron density for all N-terminal residues (the density for the Leu sidechain is somewhat lower, suggesting increased mobility relative to the backbone); middle: wild-type ISCU2 shows poor electron density at the N terminus indicating high mobility, and was modeled with two possible conformations for Tyr35; right: The mutant protein ISCU2-L35H36 shows poorer electron density for the N terminus indicating that the His36 sidechain increases mobility.
