Abstract
Sarcomeres, the basic contractile units of striated muscle cells, contain arrays of thin (actin) and thick (myosin) filaments that slide past each other during contraction. The Ig-like domain-containing protein myotilin provides structural integrity to Z-discs-the boundaries between adjacent sarcomeres. Myotilin binds to Z-disc components, including F-actin and $\alpha$-actinin-2, but the molecular mechanism of binding and implications of these interactions on Z-disc integrity are still elusive. To illuminate them, we used a combination of small-angle X-ray scattering, cross-linking mass spectrometry, and biochemical and molecular biophysics approaches. We discovered that myotilin displays conformational ensembles in solution. We generated a structural model of the F-actin:myotilin complex that revealed how myotilin interacts with and stabilizes F-actin via its Ig-like domains and flanking regions. Mutant myotilin designed with impaired F-actin binding showed increased dynamics in cells. Structural analyses and competition assays uncovered that myotilin displaces tropomyosin from F-actin. Our findings suggest a novel role of myotilin as a co-organizer of Z-disc assembly and advance our mechanistic understanding of myotilin's structural role in Z-discs.
- *protein
- and
- binding/genetics,protein
- contraction/genetics,muscle
- cultured,cytoskeletal
- cytoskeleton/chemistry/genetics/metabolism,actins/chemistry/genetics/*metabolism,animals,cells
- domains
- interaction
- motifs/genetics,sarcomeres/genetics/*metabolism,to_read,tropomyosin/chemistry/genetics/metabolism
- multimerization/genetics,actin
- proteins/chemistry/genetics/metabolism,muscle
- proteins/genetics/metabolism,cytoskeleton/metabolism,humans,mice,microfilament
- skeletal/metabolism,protein
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