Effect of a minor population of closed GlnBP conformer on the fit of PREs arising from unliganded GlnBP S51C (full lines) and D122C (dashed lines). Overall, intra-, and interdomain Q-factors are indicated in black, red, and blue, respectively. The backbone coordinates for the closed conformer are those of the liganded GlnBP crystal structure (PDB ID 1WDN).