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Figure 4.
Highlight of residues in the Ca^2+-binding loop of the
protease domain in the structures of FVIIa[D212N] (A and B; 2.7
Å) and wild-type FVIIa (C; 2.0 Å; PDB code 1DAN).
The N terminus is indicated with an arrow and hydrogen bonds
shown by dotted lines.2F[o] – F[c] electron density maps are
shown at 1σ (blue) and 2σ (red). The mutant structure shows
changes of hydrogen bond networks in the Ca^2+-binding loop
(Ca^2+ shown as a green sphere), for example, surrounding
mutated residue Asn^212 and Ser^214 and Glu^296. A hydrogen bond
is abolished between Asn^212 and Ser^214 because of a side chain
movement of Ser^214 in the mutant structure. A hydrogen bond
network is introduced between Asn^212, Glu^296, and two strongly
defined water molecules. In the wild-type structure, Asp^212 and
Glu^296 are not in an electrostatically optimal configuration
because of charge repulsion and the conformations of the two
residues are slightly changed in the mutant structure. A
distinct side chain movement of Asp^217 can be observed as well.
In turn, a hydrogen bond between Lys^161 and Asp^217 is lost,
whereas bonding to Asp^219 is strengthened: Asp^219 to Lys^161
is 2.6 Å in the mutant structure (see B) versus 3.9
Å in the wild-type structure (see C). Root mean square
displacements (Cα) of the Ca^2+-binding loop of the mutant
structure versus the wild structure were 0.74 Å compared
with an overall of 0.65 Å for the heavy chains.
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