Structure of isolated Z-disks from honeybee flight muscle

Abstract

The Z-disk is a complex structure comprising some 40 proteins that are involved in the transmission of force developed during muscle contraction and in important signalling pathways that govern muscle homeostasis. In the Z-disk the ends of antiparallel thin filaments from adjacent sarcomeres are crosslinked by α-actinin. The structure of the Z-disk lattice varies greatly throughout the animal kingdom. In vertebrates the thin filaments form a tetragonal lattice, whereas invertebrate flight muscle has a hexagonal lattice. The width of the Z-disk varies considerably and correlates with the number of α-actinin bridges. A detailed description at a high resolution of the Z-disk lattice is needed in order to better understand muscle function and disease. The molecular architecture of the Z-disk lattice in honeybee (Apis mellifera) is known from plastic embedded thin sections to a resolution of 7 nm, which is not sufficient to dock component protein crystal structures. It has been shown that sectioning is a damaging process that leads to the loss of finer details present in biological specimens. However, the Apis Z-disk is a thin structure (120 nm) suitable for cryo EM. We have isolated intact honeybee Z-disks from indirect flight muscle, thus obviating the need of plastic sectioning. We have employed cryo electron tomography and image processing to investigate the arrangement of proteins within the hexagonal lattice of the Apis Z-disk. The resolution obtained, ~6 nm, was probably limited by damage caused by the harshness of the conditions used to extract the myofibrils and isolate the Z-disks.Electronic supplementary materialThe online version of this article (doi:10.1007/s10974-017-9477-5) contains supplementary material, which is available to authorized users.

Cryo-electron tomography of cardiac myofibrils reveals a 3D lattice spring within the Z-discs

“…14 and 58 Å ref. 22 ). The resolutions of the α-actinin densities were sufficient for rigid-body docking of the crystal structure 3 (Fig.…”

“…In this study, we reported the first native 3D structure of the mammalian Z-disc. The 3D structure of the native invertebrate Z-disc has previously been reported 22 , but the invertebrate Z-discs are separated from the actomyosin system under a harsh condition (extraction using 0.6 M potassium iodide). Moreover, the reconstructed map severely suffers from the missing wedge of information because the isolated invertebrate Z-discs are uniformly oriented perpendicular to the beam axis.…”

After the revolution: how is Cryo-EM contributing to muscle research?

“…3 a Cryo-EM structure of the relaxed thick filament from Lethocerus flight muscle (EMD-3301, 5.5 Å) (Hu et al 2016). b Cryo-ET structure of frozen-hydrated honeybee Z-disk (EMD-8727, 60.0 Å) (Rusu et al 2017). Map comparisons not to scale…”

“…To calculate the 3D structure electron tomography is commonly used, where a series of images at different tilts are recorded. One of the most recent Cryo-EM structures of part of the sarcomere was from Rusu et al (2017) (Fig. 3b).…”

3-D Structure of Z-disks Isolated from the Flight Muscle of Lethocerus indicus

“…The 1,0 lattice spot is weak to absent. B) Fourier transform Z-disc from Honeybee flight muscle with strong first order diffraction[1].…”