Burgess, S.A., Yu, S., Walker, M.L., Hawkins, R.J., Chalovich, J.M. and Knight, P.J. (2007) Structures of smooth muscle myosin and heavy meromyosin in the folded, shutdown state. Journal of Molecular Biology, 372 (5). pp. 1165-1178. ISSN 0022-2836
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Remodelling of the contractile apparatus within smooth muscle cells is an essential process that allows effective contractile activity over a wide range of cell lengths. The thick filaments may be redistributed via depolymerisation into inactive myosin monomers that have been detected in vitro, in which the long tail has a folded conformation. The structure of this folded molecule has been controversial. Using negative stain electron microscopy of individual folded molecules from turkey gizzard we show they are more compact than previously described, with heads and the three segments of the folded tail closely packed. Smooth muscle heavy meromyosin (HMM), which lacks two-thirds of the tail, closely resembles the equivalent parts of whole myosin. Image processing reveals a characteristic head region morphology for both HMM and myosin whose features are identifiable by comparison with less compact molecules. The two heads associate asymmetrically: the tip of one motor domain touches the base of the other, resembling the blocked and free heads of this HMM when it forms 2-D crystals on lipid. The tail of HMM lies between the heads, contacting the blocked motor domain, unlike in the 2-D crystal. The tail of the intact myosin is bent sharply and consistently at two positions close to residues 1175 and 1535. The first bend position correlates with a skip in the coiled coil sequence, the second does not. The first segment runs between the heads from the head-tail junction. Unexpectedly, the other segments associate only with the blocked head rather than both heads, such that the second bend lies at a specific position near the C-lobe of the blocked head regulatory light chain. Quantitative analysis of tail flexibility shows that the single coiled coil of HMM has an apparent Young’s modulus of about 0.5 GPa. The folded tail of the intact molecule is less flexible indicating interactions between the segments. The folded tail does not modify the compact head arrangement but stabilises it, indicating a structural mechanism for the very low ATPase activity of the folded molecule.
|Copyright, Publisher and Additional Information:||© 2007 Elsevier B.V. This is an author produced version of a paper published in Journal of Molecular Biology. Uploaded in accordance with the publisher's self-archiving policy.|
|Keywords:||myosin, smooth muscle, regulation, electron microscopy, image processing|
|Institution:||The University of Leeds|
|Academic Units:||The University of Leeds > University of Leeds Research Centres and Institutes > Astbury Centre for Structural Molecular Biology (Leeds)
The University of Leeds > Faculty of Biological Sciences (Leeds) > School of Molecular and Cellular Biology (Leeds)
The University of Leeds > University of Leeds Research Centres and Institutes > Interdisciplinary Research Centre in Polymer Science and Technology (Leeds)
|Depositing User:||Sherpa Assistant|
|Date Deposited:||05 Nov 2007 16:34|
|Last Modified:||17 Aug 2015 13:36|