Three-Dimensional Structure of Vertebrate Muscle Z-Band: The Small-Square Lattice Z-Band in Rat Cardiac Muscle. Issue 22 (6th November 2015)

• Record Type: Journal Article
• Authors: Burgoyne, Thomas; Morris, Edward P.; Luther, Pradeep K.
• Is Part Of: Journal of molecular biology. Volume 427:Issue 22(2015:Nov. 15)
• Page Start: 3527
• Page End: 3537
• Publication Date: 2015-11-06
• Subjects: 3D three-dimensional -- 2D two-dimensional -- FT Fourier transform; electron tomography -- electron microscopy -- Z-line -- Z-disc -- α-actinin; Molecular biology -- Periodicals; Biology -- Periodicals; Biochemistry -- Periodicals; Bacteriology -- Periodicals; Molecular Biology -- Periodicals; Biochemistry -- Periodicals; Biologie moléculaire -- Périodiques; Biologie -- Périodiques; Biochimie -- Périodiques; Moleculaire biologie; Biochemistry; Biology; Molecular biology; Periodicals; 572.805
• DOI: 10.1016/j.jmb.2015.08.018
• Languages: English
• ISSNs: 0022-2836

Abstract

Abstract: 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 5–7 nm 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. Graphical abstract: Highlights: 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 5–7 nm of the actin filament within the Z-band is devoid of links and may be due to capping protein CapZ.