Fig. 6: Structure of full-length apo-MaeB reveals a large-scale rotation governs allostery.
From: A rotary mechanism for allostery in bacterial hybrid malic enzymes
A Structure of MaeBapo. The PTA hexameric “hub” retains the conformation observed in the isolated PTA apo form, and the ME dimer rotates relative to this to place the hook subdomain under the PTA d1 region. This rotation is enabled by a different L1:L2 juxtaposition that places L1 directly below L2. B Comparison of the apo (left) and bound (right) linker regions. The helical character of this region is retained in MaeBapo, but an alteration in the loop between L1 and L2 results in the lower face of L2 (V441, R444, N448) interacting with L1 (acidic patch of D426, E430, E433) rather than the interactions with the ME domain observed in MaeBbound. C The rotation of the ME dimer in MaeBapo allows the hook subdomain to adopt a folded conformation, wherein it interacts with PTA d1. D Comparison of PTA conformational change between MaeBapo (yellow) and MaeBbound (grey). The d1:d2 flexation is essentially similar to that observed for the isolated PTA structures, but with the additional outcome that the linker region is remodelled in response to changes at the d1:d2 hydrophobic core (zoomed in righthand panel). E Mechanism of rotation of ME domain, viewed from two separate orientations. A direct comparison of MaeBapo and MaeBbound, with an overlay obtained from PTA superposition (removed for clarity), reveals that the PTA:linker (labelled “to PTA”, coloured red) is in the same relative location in both forms but the ME domain pivots 70° about the twofold axis. The L-shaped L1:L2 orientation in MaeBbound is replaced by the co-linearity of MaeBapo, swinging the ME fold relative to the pivot axis—a representative ME feature below the linker (α-helix 400–414) is coloured red to assist in the interpretation of this movement. Also refer to Supplementary Movie 1. F Resultant difference in shape of the MaeBapo and MaeBbound hexamers. Rotation of the ME dimers in the apo form results in a more streamlined disc-shape, given that the ME domains now align with the PTA hexamer d2:d2 edge. G Overlay of MaeBapo (transparent) and MaeBbound. Flexation at the PTA hub rotates three ME dimers at each flat edge of the triangular array.
