Three-Dimensional Structure of Vertebrate Muscle Z-Band: The Small-Square Lattice Z-Band in Rat Cardiac Muscle

• Published in: Journal of molecular biology Vol. 427; no. 22; pp. 3527 - 3537
• Main Authors: Burgoyne, Thomas, Morris, Edward P., Luther, Pradeep K.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 06.11.2015; Elsevier
• Subjects: Actin Cytoskeleton - metabolism; Actinin - metabolism; Animals; Connectin - metabolism; Cytoskeleton - metabolism; electron microscopy; electron tomography; Microscopy, Electron; Models, Molecular; Muscle Proteins - metabolism; Myocardium - chemistry; Myocardium - metabolism; Myocardium - ultrastructure; Rats; Sarcomeres - chemistry; Sarcomeres - metabolism; Sarcomeres - ultrastructure; Z-disc; Z-line; α-actinin; 3D; 2D; α-actinin; Z-disc; Z-line; electron microscopy; electron tomography; FT
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2015.08.018

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 α-actinin, linking antiparallel overlapping ends of the actin filaments from the adjoining sarcomeres. The reconstruction shows that the terminal 5–7nm of the actin filaments within the Z-band is devoid of any α-actinin links and is likely to be the location of capping protein CapZ. [Display omitted] •The vertebrate muscle Z-band connects antiparallel actin filaments from two adjacent sarcomeres.•Contractile tension is transmitted via α-actinin linking the antiparallel actin filaments.•We have used electron tomography and subtomogram averaging to investigate the three-dimensional structure of the Z-band in rat cardiac muscle.•The Z-band is composed of overlapping ends of actin filaments crosslinked by four to six layers of α-actinin.•The terminal 5–7nm of the actin filament within the Z-band is devoid of links and may be due to capping protein CapZ.