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Figure 6.
Figure 6. Shape adaptation upon binding of arthropod
trypsin inhibitor SGTI to the surface of crayfish trypsin. (a)
The structural alignment of the free (rose) and bound (light
blue) forms of SGTI reveals three regions of major backbone
conformation difference: the N-terminal segment (not shown),
residues 20-26 (P[10]-P[4]) and residue 31 (P[2]'). The latter
two are parts of the binding region (O and N atoms shown in
atomic colors). Carbon atoms of residues in the P[7]-P[4] and
P[2]' regions are colored orange and dark blue for the free and
bound form of SGTI, respectively. (b) Cartoon of SGTI binding to
the enzyme. SGTI is shown in light blue (segments of the binding
region with different backbone conformations in the free and
bound form) and black (remaining parts). Cysteine and P[1]
arginine side-chains of SGTI are shown, while some of its
sub-sites are labeled in red. The enzyme surface is shown in
magenta with black labels for the substrate binding sub-sites.
Upper panel: conformation of the free form is preformed to
recognize the S[12]-S[8] and S[4]'-S[5]' sub-sites of the enzyme
(shown as broken green arrows). In regions P[10]-P[4] and P[2]'
conformation changes should occur, causing the rotation of the
P[3]-P[1]' and P[4]'-P[5]' as well (light blue arrows). Lower
panel: these conformational changes facilitate the build-up of
an extended interaction network between SGTI and the enzyme
(green arrows) in the complex.
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