|
Figure 1.
Figure 1 Important features of the myosin VI motor. (A) The
different elements of the myosin VI motor are shown in the
rigor-like myosin VI structure (Ménétrey et al,
2005). The motor domain is composed of four subdomains (Nter,
U50, L50 and the converter). The converter (green) is the most
mobile of these and is directly linked to the lever arm. In
myosin VI, the converter interacts with a unique inserted
structural element (insert 2; purple). This redirects the lever
arm in the opposite direction from plus-end myosins. The central
beta-sheet (gray and blue) is the major component of the
transducer, which can adopt differently twisted conformations
depending on the nucleotide- and actin-binding states of the
motor. There are three nucleotide-binding elements: P-loop,
switch I and switch II. Rotation of the converter is controlled
by the rearrangements of the relay (yellow) and the SH1-helix
(red). (B) Diagram illustrating the converter (green) and the
lever arm (purple for the insert 2-CaM-binding region and cyan
for the IQ-CaM) position in three states of the myosin VI motor
cycle. The motor domain is composed of an SH3 domain (black
ball) and four subdomains (N-terminal (Nter, gray), upper 50 kDa
(U50, blue), lower 50 kDa (L50, light gray) and converter). The
relay (yellow) and SH1-helix (red) are two connectors of the
motor that direct the rotation of the converter. The powerstroke
corresponds to the large (11 nm) movement of the lever arm
between the pre-powerstroke (PPS, 2V26) and rigor state (2BKH),
during which the converter both rotates and alters its
conformation. ATP binding in the rigor state induces
rearrangements in the motor to detach the motor from actin and
produce the post-rigor state. To optimize the powerstroke, no
reversal of the lever arm movement should occur upon ATP binding
and myosin detachment from actin. However, it is not clear that
this can be accomplished for myosin VI, since it is unclear what
happens to the converter conformation and lever arm position
following ATP binding.
|
