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Figure 2.
Figure 2. Structural comparison of native aequorin,
semi-synthetic aequorins, and calmodulin. (A) Superimposed
structures of molecule A of native aequorin and semi-synthetic
aequorins. Native, cp-, br-, i-, and n-aequorin are shown in
yellow, pink, blue, sky blue, and green, respectively.
Apoaequorins are shown as C  trace models.
Coelenterazine moieties are drawn as ball-and-stick models with
same colors as above. The coelenterazine moiety and the loop
region of EF-hands I, III, and IV are surrounded by red, light
blue, green, and orange circles, respectively. W1 in native
aequorin is drawn as a sphere model in cyan. The OH group of the
2-substituent of native coelenterazine is stabilized by a
hydrogen-bonding network mediated by W1. W1 is absent in br-,
i-, and n-aequorin. The cyclopentyl group at the C8 position of
cp-coelenterazine can make neither a stacking interaction with
Lys39 nor a  - interaction with
Trp108. This figure was prepared with MolScript (Kraulis 1991)
and Raster3D (Merrit and Bacon 1997). (B) Superimposed
structures of EF-hands I, III, and IV of aequorin. (1) The
superimposed structures of EF-hands I (shown in sky blue circle
in Fig. 2A: 20-37), III (shown in green circle in Fig. 2A:
113-130), and IV (shown in orange circle in Fig. 2A: 149-166).
EF-hand IV in molecule A is colored cyan and EF-hand IV in
molecule B is colored blue. EF-hands I and III are colored green
and yellow-green, respectively. The blue dashed line, EF-IV(B2),
is the loop structure of EF-hand-IV(B) superimposed onto the
same region of EF-IV(A). (2) The superimposed structures of the
EF-hand I loop (residues 20-37) of aequorin (green) and
Ca^2+-bound (deep pink) and Ca^2+-unbound (cream) calmodulin.
The Ca^2+ is drawn as a sphere. All figures were prepared with
MolScript (Kraulis 1991). (C) Structure comparison between
aequorin and calmodulin. The superimposed structures of aequorin
(yellow-green) and Ca^2+-unbound calmodulin (cream). The traced
region of aequorin is from Thr103 to Pro189. The traced region
of calmodulin is from Ser81 to Lys148. The coelenterazine moiety
(CZH) is drawn as a ball-and-stick model. Dashed lines appeared
in the inside of the red circle are main-chain interactions,
green dotted lines are interactions in aequorin, and cream ones
are interactions in calmodulin.
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