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Figure 3.
Figure 3. Stereo views of the active site region. a, Domain
III of monomer C was superimposed on domain III of the 67 kDa
fragment to illustrate the changes around Tyr 319. The structure
of the 67 kDa fragment is colored by atom type; monomer C is
colored green. Arg 321 is unable to interact with Tyr 319 in the
67 kDa fragment, as it forms hydrogen bonds to the acidic
residues in domain I, but the arginine residue has moved in the
30 kDa fragment, and the side chain guanidinium group makes
hydrogen bonds to the active site tyrosine. This suggests that
Arg 321 could play a role in stabilizing an activated tyrosine.
Water molecules were not drawn for clarity. This diagram was
prepared using MOLSCRIPT^13 and RASTER3D^14, ^15. b, Electron
density maps showing the active site region in the hexagonal
crystal form. The 2F[o] - F[c] map is colored in cyan and is
contoured at the 1.5  level,
while the F[o] - F[c] map is colored in magenta and is contoured
at the +3 level.
The difference map clearly shows the presence of a second
conformation for Arg 321. c, Electron density map showing the
active site region in the monoclinic crystal form. The 2F[o] -
F[c] map is colored in cyan and is contoured at the 1.5 level.
Maps (b) and (c) were prepared using BOBSCRIPT^16 and
RASTER3D^14, ^15.
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