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Figure 4.
FIG. 4. Close-up of active site residues. The initial F[o]
- F[c] electron density maps are overlaid the apoDPP-IV (A),
Y547F mutant (B), and complex DFP·DPP-IV (C, slightly
different view, relative to A and B) contoured at 2  (cyan),
3 (red), 5 (purple,
only contoured in the apo structure), and 8 (blue, only contoured
in the DFP structure). The initial 2F[o] - F[c] electron density
map is overlaid the complex DFP·DPP-IV contoured at 1
(gray). Structural
inspections of the active site of the Y547F mutant reveals a
missing water molecule, clearly seen in the wild type apo
structure (i.e. hydrogen bonds between Tyr547-OH, Ser630-OH, and
Tyr631-NH are indicated). The mutated residue (Phe^547) is
positioned exactly as the tyrosine residue. The water molecule
designated Wat258 and Wat421 in the apo and the Y547F mutant
structure, respectively, is moved 0.5 Å away from the 547
residue and 0.3 Å (2.9 versus 3.2 Å) closer to the
neighboring Tyr666-OH (not shown) in the mutant structure. The
complex between DFP and DPP-IV showed that the organophosphorous
inhibitor was covalently bound to Ser630, mimicking the
tetrahedral intermediate.
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