Abstract
Here we solve a 2.4-Å structure of a truncated version of the reverse-direction myosin motor, myosin VI, that contains the motor domain and binding sites for two calmodulin molecules. The structure reveals only minor differences in the motor domain from that in plus-end directed myosins, with the exception of two unique inserts. The first is near the nucleotide-binding pocket and alters the rates of nucleotide association and dissociation. The second unique insert forms an integral part of the myosin VI converter domain along with a calmodulin bound to a novel target motif within the insert. This serves to redirect the effective ‘lever arm’ of myosin VI, which includes a second calmodulin bound to an ‘IQ motif’, towards the pointed (minus) end of the actin filament. This repositioning largely accounts for the reverse directionality of this class of myosin motors. We propose a model incorporating a kinesin-like uncoupling/docking mechanism to provide a full explanation of the movements of myosin VI.
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Acknowledgements
We thank the staff of the European Synchrotron Radiation Facility for assistance during data collection, A. Li and D. Garbett for technical assistance in preparing the recombinant proteins, and J. Cicolari for assistance in crystallization experiments. This work was supported by a grant from the National Institutes of Health (NIAMS) to H.L.S and A.H., grants from the CNRS and the ARC to A.H., and predoctoral fellowships from the Quebec government and the FRM to A.B.
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Atomic coordinates and structure factors have been deposited in the Protein Data Bank under the accession numbers 2BKH and r2bkhsf for MDins2 and 2BKI and r2bkisf for long MDins2IQ. Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
Supplementary information
Supplementary Methods
Additional information on the methods used in this study. (DOC 78 kb)
Supplementary Data
Analysis of the role of insert1 in myosin VI kinetics. (DOC 41 kb)
Supplementary Table S1
Steady-state and transient kinetic parameters of myosin VI short MDins2IQ with and without insert-1. (DOC 33 kb)
Supplementary Table S2
Data collection and refinement statistics (DOC 53 kb)
Supplementary Figure S1
Lever arm of myosin VI MDins2IQ. Shown is a ribbon representation of the lever arm of the myosin VI MDins2IQ structure. The electron density map clearly shows that the long heavy chain helix found for the insert2 sequence (dark purple) remains straight and extends to form the first part of the IQ motif (cyan), which binds the C-terminal semi-open lobe of an apo-calmodulin (yellow). Variability is however observed in the orientation of the second part of the IQ motif and in most of the helices of the N-terminal lobe of its associated CaM. These regions of higher disorder were not included in the final coordinates and are shown in white in this figure. They are modelled using the coordinates of a Ca2+-free CaM bound to the first IQ motif from mouse myosin V (A.H. unpublished data). (PDF 1360 kb)
Supplementary Movie S1
The 50kDa cleft is not totally closed in this structure of the nucleotide-free Myosin VI motor. Cleft closure occur via interactions between the U50kDa (blue) and L50kDa (white) residues on either side of the cleft. These are only found in the rigor-like myosin V structure. The cleft is totally open in the myosin V post-rigor state. In the myosin VI structure, the cleft is slightly more closed than that of the Dictyostelium discoideum myosin II structure in the absence of nucleotide, but these two structures differ from the myosin V structure and do not correspond to the rigor-like state. (GIF 762 kb)
Supplementary Movie S2
The distortion of the central β-sheet that controls rearrangements in the myosin motor domain differs between Myosin V and VI. (GIF 342 kb)
Supplementary Movie S3
The SH1 helix / N-terminal subdomain interface differs between Myosin V and VI. (GIF 501 kb)
Supplementary Movie S4
Directionality and power-stroke in myosin motors. Animation related to Figure 5. (GIF 1547 kb)
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Ménétrey, J., Bahloul, A., Wells, A. et al. The structure of the myosin VI motor reveals the mechanism of directionality reversal. Nature 435, 779–785 (2005). https://doi.org/10.1038/nature03592
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DOI: https://doi.org/10.1038/nature03592
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