Supplementary Figure 4: Ternary-complex electron density maps, alternate conformations and comparison with porcine ST3GalI.
From: Structure of human ST8SiaIII sialyltransferase provides insight into cell-surface polysialylation
(a) Simulated annealing omit map of monomer A of the ternary complex (calculated with PHENIX in absence of donor and acceptor at 2.3 Å resolution; 2mFo-DFc (blue) contoured at 1σ, mFo-DFc (green) at 3σ, acceptor Sia-6S-LacNAc orange, donor analogue CMP-3FNeu5Ac dark green with disordered atom positions indicated at 85% transparency, His354 magenta. (b) Omit electron density of monomer B of the ternary complex (coloring see a). (c) Refined electron density map of monomer A (2mFo-DFc blue at 1σ, mFo-DFc green at 3σ). (d) Refined electron density map of monomer B (coloring see a). (e) Close-up on the simulated annealing omit map of the donor in monomer A of the ternary complex (coloring as in a). (f) Close-up on the simulated annealing omit map of the donor CMP-3FNeu5Ac in monomer B of the ternary complex (coloring as in a). (g) Overlap of Sia-6S-LacNAc of monomer A (yellow) on Sia-6S-LacNAc of monomer B (orange, r.m.s.d. 0.8 Å on all atoms) of the ternary complex. Note the different conformations of the glycerol group (black circle), with Sia-6S-LacNAc of monomer B exhibiting the catalytically permissive conformation for the C8 hydroxyl group. (h) Composite view of ternary complex of ST8SiaIII with CMP-3FNeu5Ac (monomer A) and Sia-6S-LacNAc (Sia-6S-LacNAc of monomer B, r.m.s.d of 0.8 Å to all atoms of Sia-6S-LacNAc of monomer A). (i) ST3GalI bound to acceptor and CMP23 (blue, PDB 2WNB).
