Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 427, Issue 22, Pages 3527-3537Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2015.08.018
Keywords
electron tomography; electron microscopy; Z-line; Z-disc; alpha-actinin
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Funding
- British Heart Foundation
- British Heart Foundation [RG/11/21/29335]
- British Heart Foundation [RG/11/21/29335, PG/07/076/23480] Funding Source: researchfish
- Cancer Research UK [16749] Funding Source: researchfish
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The Z-band in vertebrate striated muscle crosslinks actin filaments of opposite polarity from adjoining sarcomeres and transmits tension along myofibrils during muscular contraction. It is also the location of a number of proteins involved in signalling and myofibrillogenesis; mutations in these proteins lead to myopathies. Understanding the high-resolution structure of the Z-band will help us understand its role in muscle contraction and the role of these proteins in the function of muscle. The appearance of the Z-band in transverse-section electron micrographs typically resembles a small-square lattice or a basketweave appearance. In longitudinal sections, the Z-band width varies more with muscle type than species: slow skeletal and cardiac muscles have wider Z-bands than fast skeletal muscles. As the Z-band is periodic, Fourier methods have previously been used for three-dimensional structural analysis. To cope with variations in the periodic structure of the Z-band, we have used subtomogram averaging of tomograms of rat cardiac muscle in which subtomograms are extracted and compared and similar ones are averaged. We show that the Z-band comprises four to six layers of links, presumably alpha-actinin, linking antiparallel overlapping ends of the actin filaments from the adjoining sarcomeres. The reconstruction shows that the terminal 5-7 nm of the actin filaments within the Z-band is devoid of any alpha-actinin links and is likely to be the location of capping protein CapZ. (C) 2015 The Authors. Published by Elsevier Ltd.
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