Figure 3.
Models of sterically hindered Gd-HOPO complexes attached to the interior MS2 surface. Structures attached to two adjacent Cys87 groups were minimized simultaneously using MacroModel, and three different coordination isomers were considered for each. The Gd coordination spheres were based on the crystal structure reported in reference 43. Representative structures are shown here, with the full set appearing in Supporting Information Figures S5 and S6. Overlays of S,S (Gd-7b, gray) and R,R (Gd-7c, brown) complexes are shown for (a) a top view and (b) a side view. The rigid linker of S,S-complex Gd-7b (c and e) forces an upright conformation that leaves the water molecules (yellow) unobstructed. R,R-complex Gd-7c (d and f) places the water molecules much closer to the capsid surface, likely restricting their exchange. The Cys 87 attachment points are shown in green in c-f.