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Figure 3.
Figure 3. Conserved and Variable Features of the Rigor-like
50 kDa Cleft
(A–E) The schematic S1 inset on this and
subsequent figures shows the region that is magnified (box) and
the viewpoint (arrow). Squid sequence numbering is used. (A)
Displayed are selected interactions between the upper (dark
green) and lower (light green) 50 kDa subdomains made in the
squid rigor-like structure that are also made (with identical or
homologous residues) in the other isoforms studied when the
corresponding part of their cleft is also fully closed.
Interactions include H-bonded/electrostatic contacts (dotted
lines) and extensive burial of certain apolar residues
(underlined labels). (B–E) Variations in crosscleft contacts,
as well as in the orientations of the upper and lower 50 kDa
subdomains or of subregions within them, help determine the
extent of inner and outer cleft closure in the various isoforms
(the green, dashed line shows squid for comparison.) (B) Myosin
V displays the most closed cleft in the strut region (also see
Table 1), perhaps due to a “complex H-bond link” (blue,
dotted lines) between Asn424, Lys601, and Glu598 not seen in any
other isoform; position 598 is aspartate in squid and sea
scallop, and 424 is serine in Dictyostelium (see below for
myosin VI). (C) A slightly modified orientation of helix HR
relative to helix HQ yields a fully closed outer but
incompletely closed inner cleft in catch and striated sea
scallop S1. (D) Curvature of helix HO about a
Dictyostelium-specific glycine at 435 contributes to its fully
closed inner but partially open outer cleft. (E) The entire
cleft of myosin VI is incompletely closed. A myosin VI-specific
lysine at position 650 appears to disrupt the interdomain
602-274-431 complex salt link made from the strut.
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