Figure 4

Microphage migration inhibition factor and C-terminal domain of arginine repressor. A new circular permutation discovered between a) the microphage migration inhibition factor (MIF, PDB ID 1uiz, chain A, top) and the C-terminal domain of arginine repressor (AR, 1xxa, chain C, bottom). a) These two proteins superimpose well spatially, with a RMSD of 1.74Å for an alignment length of 24 residues, and a p-value of 1.3 × 10^-2. b.) These proteins are related by a circular permutation. The loop connecting helix 1 with strand 2 of MIF (in rectangle, top) becomes disconnected in arginine repressor, the N- and C- termini of MIF (in ellipse, top) becomes connected in arginine repressor (in ellipse, bottom). The disconnection of helix 1 from strand 2 of MIF removes some spatial constraints, allowing strand 1' in AR to swap places with strand 4'. c) The topology diagram of these two proteins. d.) The artificial topology diagram for arginine repressor, where strand 2' and strand 4' are spatially swapped back. The diagram for AR in (c) has the same topology as the diagram in (d).