title: Three-Dimensional Structure of Vertebrate Muscle Z-Band: The Small-Square Lattice Z-Band in Rat Cardiac Muscle.
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 5-7nm 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.
authors.affiliation: University College London, London WC1E 6BT, United Kingdom.
authors.forename: Thomas
authors.initials: T
authors.lastname: Burgoyne
authors.affiliation: Institute of Cancer Research, London SW7 3RP, United Kingdom.
authors.forename: Edward P
authors.initials: EP
authors.lastname: Morris
authors.affiliation: Imperial College London, London SW7 2AZ, United Kingdom. Electronic address: p.luther@imperial.ac.uk.
authors.forename: Pradeep K
authors.initials: PK
authors.lastname: Luther
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000185:Actinin / Q000378:metabolism; D000818:Animals; D064211:Connectin / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism*; D008854:Microscopy, Electron; D008958:Models, Molecular; D009124:Muscle Proteins / Q000378:metabolism; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D051381:Rats; D012518:Sarcomeres / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: D064211:Connectin; D009124:Muscle Proteins; D000185:Actinin
keywords: Z-disc; Z-line; electron microscopy; electron tomography; α-actinin