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Figure 2.
Figure 2. Comparison of the Rigor-like and Post-Rigor States
of Muscle Myosin S1 and Its Active Site
(A and B) Detailed
legends for all figures are supplied in Supplemental Data. (A)
Schematic overlay of (squid) S1 in the two states (see text).
The rigor-like state is shown in green, and the post-rigor state
is shown in red. Thicker lines indicate proximity to the reader.
The overall conformational differences between these (and the
pre-power stroke) states are generally conserved in the
different isoforms. The locations of interdomain interactions
that nevertheless appear to preferentially stabilize the
high-duty ratio non-muscle myosin V in a rigor-like conformation
and some of the low-duty ratio myosin II isoforms in a
non-rigor-like (actin-detached) conformation are indicated here
with blue and red asterisks, respectively (also see text and
Figure 3, Figure 4 and Figure 5). (B) The rigor-like location of
switch II in the various myosin II and VI structures (green),
which have small side chains at (squid) position 465, differs
from that in myosin V (blue), in which 465 is a tyrosine. The
locations of both switch I and switch II away from the
nucleotide and near each other force the tyrosine to adopt a
“g−” rotamer. The myosin V switch II is displaced toward
the P loop of the N-terminal subdomain in the rigor-like state
to avoid a clash of this rotamer with helix W (not shown). In
the post-rigor state (red), switch I (including Ser246) is near
the nucleotide and relatively far from switch II. Here, the
tyrosine has room to adopt the “g+” rotamer and does not
perturb the arrangement of the active site elements.
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