Shuttling of the chaperones Unc45b and Hsp90a between the A band and the Z line of the myofibril.
The formation of thick filaments in striated muscle involves the chaperones Hsp90a and Unc45. We show that Unc45b and Hsp90a, two zebrafish orthologues, colocalize with myosin during myofibrillogenesis and associate with the Z line when myofibril assembly is completed. In response to stress or damage to the myofiber, Unc45b and Hsp90a dissociate from the Z line and transiently associate with myosin. Although chaperone activity of Unc45b requires the full-length protein, only the central and Unc45-Cro1p-She4p domains are required to anchor it to the Z line, and multiple subdomains mediate association with nascent myosin. We propose that the Z line serves as a reservoir for chaperones, allowing a rapid mobilization in response to muscle damage. Our data are consistent with a differential affinity model as an explanation for the shuttling of the chaperones between the Z line and myosin.
Etard
Christelle
C
Institute for Toxicology and Genetics, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany.
Roostalu
Urmas
U
Strähle
Uwe
U
D000818:Animals; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism* / Q000648:ultrastructure; D008954:Models, Biological; D018832:Molecular Chaperones / Q000378:metabolism*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000648:ultrastructure; D009124:Muscle Proteins; D054792:Muscle, Striated / Q000293:injuries / Q000378:metabolism* / Q000648:ultrastructure; D009218:Myosins / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D012038:Regeneration / Q000502:physiology; D013314:Stress, Mechanical; D013997:Time Factors; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000378:metabolism*
D018841:HSP90 Heat-Shock Proteins; D018832:Molecular Chaperones; D009124:Muscle Proteins; C472790:Unc45b protein, zebrafish; D029961:Zebrafish Proteins; D009218:Myosins