The M-band: an elastic web that crosslinks thick filaments in the center of the sarcomere

The sarcomere of striated muscle is an efficient molecular machine, characterized by perfect structural organization of contractile filaments. This order is ensured by the sarcomere cytoskeleton, an important element of which is the M-band, believed to maintain the thick filament lattice. We review...

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Bibliographic Details
Published in:Trends in cell biology 2005-09, Vol.15 (9), p.477-485
Main Authors: Agarkova, Irina, Perriard, Jean-Claude
Format: Article
Language:English
Subjects:
Animals
Connectin
Elasticity
Humans
Microscopy, Electron
Models, Biological
Muscle Contraction - physiology
Muscle Proteins - physiology
Muscle, Skeletal - physiology
Muscle, Skeletal - ultrastructure
Myofibrils - physiology
Myofibrils - ultrastructure
Myosins - physiology
Protein Isoforms - physiology
Protein Kinases - physiology
Sarcomeres - physiology
Sarcomeres - ultrastructure
Stress, Mechanical
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Summary:The sarcomere of striated muscle is an efficient molecular machine, characterized by perfect structural organization of contractile filaments. This order is ensured by the sarcomere cytoskeleton, an important element of which is the M-band, believed to maintain the thick filament lattice. We review here recent progress in understanding the M-band function and its structural organization. We explain how the M-band might reduce the intrinsic instability of thick filaments and help titin to maintain order in the sarcomeres. The M-band molecular structure has been clarified recently by biochemical and biophysical approaches that focused on the properties of the prominent M-band component myomesin. These have shown that antiparallel myomesin dimers might link the thick filaments in the M-band, a role analogous to that of α-actinin in the Z-disc. Furthermore, similar to titin, myomesin is a molecular spring with complex visco-elastic properties that can be modified by alternative splicing. M-band protein composition correlates with the expression of titin isoforms and appears to be a reliable marker for biomechanical conditions in contracting muscle. We propose that the M-band is in fact a dynamic structure that monitors the stress appearing in the thick filament lattice during contraction and quickly reorganizes to meet new physiological requirements.
ISSN:0962-8924
1879-3088
DOI:10.1016/j.tcb.2005.07.001