(a) Stereoview of the active site of FPP synthase from E. coli complexed with IPP (C = green, O = red, and
P = yellow) and the unreactive substrate analogue DMSPP (C = brown
and S = yellow) reveals the binding of a full complement of 3 Mg2+ ions (blue spheres 1, 2, and 3). Metal coordination and
hydrogen bond interactions are indicated by solid blue and dotted
red lines, respectively. (b) Alternative orientation of the complex
shown in (a) reveals that the diphosphate group of DMSPP, which ultimately
becomes coproduct inorganic pyrophosphate, is suitably oriented to
serve as the catalytic general base that mediates stereospecific deprotonation
of the pro-R proton at C2 of IPP. Originally published
in ref (65). Copyright
2004 American Society for Biochemistry & Molecular Biology.