Myosin X forms an
antiparallel dimer and moves processively on
actin bundles. How the antiparallel dimer affects the stepping mechanism
of myosin X remains elusive. Here, we generated several chimeras using
domains of myosin V and X and performed single-molecule motility assays.
We found that the chimera containing the motor domain from myosin
V and the lever arm and antiparallel coiled-coil domain from myosin
X has multiple forward step sizes and moves processively, similar
to full-length myosin X. The chimera containing the motor domain and
lever arm from myosin X and the parallel coiled-coil from myosin V
takes steps of ∼40 nm at lower ATP concentrations but was nonprocessive
at higher ATP concentrations. Furthermore, mutant myosin X with four
mutations in the antiparallel coiled-coil domain failed to dimerize
and was nonprocessive. These results imply that the antiparallel coiled-coil
domain is necessary for multiple forward step sizes of myosin X.
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