Figure 1.
Fig. 1. Overview of the internally uncoupled scallop S1
conformation. (A) (Center) The internally uncoupled
S1-ADP·BeF[x] structure (50-kDa upper subdomain is shown
in red, 50-kDa lower subdomain is shown in pink, N-terminal
subdomain is shown in blue, converter is shown in green, lever
arm heavy chain is shown in purple, essential light chain is
shown in cyan, regulatory light chain is shown in magenta).
Notable features of the structure include the unusual position
of the lever arm and the unwound SH1 helix. Three other scallop
structures (S1-AMPPNP, S1-ATP[ -S]-p-PDM,
and S1-ADP-p-PDM), as well as the previously reported scallop
S1-MgADP (1), show the same conformation, although the
orientations of the respective lever arms vary slightly. (Right
Inset) Expanded view of the nucleotide binding size. (Left)
Schematic diagram of the internally uncoupled conformation,
showing the subdomains and the approximate location of the
disordered SH1 helix (light chains not shown). (B) For
comparison, a two-dimensional projection of the three weak
actin-binding S1 conformations observed in scallop crystal
structures (light chains not shown) (1, 2). The 50-kDa upper and
N-terminal subdomains of the three structures are superimposed
to show the large changes in the relative positions of the
converter and lever arm (see also ref. 2). In each conformation,
the 50-kDa lower subdomain adopts a slightly different position
with respect to the 50-kDa upper and N-terminal subdomains,
leading to a markedly different orientation of the converter.
The converter, in turn, controls the position of the lever arm
(1). Movement of the 50-kDa lower subdomain is not represented
in this schematic diagram. This subdomain rotates to maintain
contact with the converter as S1 adopts each of the three
conformations. See Fig. 5 for a more detailed three-dimensional
description of the subdomain motions.
-S]-p-PDM,
and S1-ADP-p-PDM), as well as the previously reported scallop
S1-MgADP (1), show the same conformation, although the
orientations of the respective lever arms vary slightly. (Right
Inset) Expanded view of the nucleotide binding size. (Left)
Schematic diagram of the internally uncoupled conformation,
showing the subdomains and the approximate location of the
disordered SH1 helix (light chains not shown). (B) For
comparison, a two-dimensional projection of the three weak
actin-binding S1 conformations observed in scallop crystal
structures (light chains not shown) (1, 2). The 50-kDa upper and
N-terminal subdomains of the three structures are superimposed
to show the large changes in the relative positions of the
converter and lever arm (see also ref. 2). In each conformation,
the 50-kDa lower subdomain adopts a slightly different position
with respect to the 50-kDa upper and N-terminal subdomains,
leading to a markedly different orientation of the converter.
The converter, in turn, controls the position of the lever arm
(1). Movement of the 50-kDa lower subdomain is not represented
in this schematic diagram. This subdomain rotates to maintain
contact with the converter as S1 adopts each of the three
conformations. See Fig. 5 for a more detailed three-dimensional
description of the subdomain motions.