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Figure 1.
Figure 1. Stabilizing Interactions in the So-Called "Pliant
Region"--the MD/Lever Arm Junction--in Scallop S1(A) Displayed
here is a schematic comparison between the pliant regions of the
chicken smooth muscle MDE-MgADP·AlF[4] structure (Dominguez et
al., 1998) (gray, only the lever arm is shown) and scallop
S1-MgADP·VO[4] (the lever arm and motor domain are shown). These
structures are superimposed by fitting the residues (765-773)
immediately N-terminal to the "pliant region." The pliant region
is straight in all scallop S1 structures but is bent in the
chicken smooth muscle crystal structure (Dominguez et al., 1998)
(also see text). The lever arm heavy chain is shown as a ribbon
diagram in purple, and the motor domain is shown schematically
with its subdomains (the 50 kDa upper and lower subdomains in
red and pink, the N-terminal subdomain in blue, the converter in
green, and the pliant helix in yellow).(B) As in (A) but from a
perpendicular view and also showing the scallop light chains
schematically (ELC in magenta, and RLC in light blue).(C)
Magnified view of the pliant region of scallop S1 (in the same
orientation as in [B] and including the ELC in magenta) shows
the side chain interactions that appear to restrain the scallop
pliant region from bending (salt bridges in red dashed lines,
van der Waals contacts in blue dashed lines). These interactions
are absent from the smooth muscle MDE crystal structure as a
result of amino acid sequence differences from scallop myosin.
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