Figure 5.
Figure 5: Directionality of movement and power stroke in myosin
motors. a, b, Schematic drawings of the myosin VI (a) and
myosin V (b) structural models (see Methods) before and after
force generation. Similar colours to those in Fig. 1 are used.
Note in particular how conformational changes in the relay
(yellow) and SH1 helix (red) lead to the rotation (black arrow)
of the converter (green). The red arrow represents the predicted
F-actin displacement (stroke) for these models; the green arrow
indicates the converter contribution for this stroke. c, For
reverse myosin I, the solid arrow indicates the stroke that
would be produced with a lever arm of about 4 nm (that
equivalent to one IQ motif) and the dotted arrow corresponds to
the stroke generated by an approximately 14-nm lever arm as
described for this engineered motor28. d, e, Two mechanisms
could account for the 12-nm
stroke of the myosin VI MD^ins2IQ. If the converter remains
coupled to the motor domain (d), it must adopt an orientation
that differs by about 90° from that found for plus-end motors in
the pre-powerstroke state. Alternatively, unwinding of the SH1
helix in the weak actin-binding states would decouple the
converter from the motor domain (e). In this case, the relay
-converter interactions would be maintained but the relay helix
would not be bent in the pre-powerstroke state because steric
clashes with the SH1 helix are eliminated. Thus, the converter
would be biased towards the plus end of the actin filament.
Recoupling of the converter to the motor domain would occur on
strong binding to actin.
The above figure is reprinted
by permission from Macmillan Publishers Ltd:
Nature
(2005,
435,
779-785)
copyright 2005.
12-nm
stroke of the myosin VI MD^ins2IQ. If the converter remains
coupled to the motor domain (d), it must adopt an orientation
that differs by about 90° from that found for plus-end motors in
the pre-powerstroke state. Alternatively, unwinding of the SH1
helix in the weak actin-binding states would decouple the
converter from the motor domain (e). In this case, the relay
-converter interactions would be maintained but the relay helix
would not be bent in the pre-powerstroke state because steric
clashes with the SH1 helix are eliminated. Thus, the converter
would be biased towards the plus end of the actin filament.
Recoupling of the converter to the motor domain would occur on
strong binding to actin.