Year-end Sale % OFF 
Abstract
Myosin folding and assembly in striated muscle is mediated by the general chaperones Hsc70 and Hsp90 and a myosin specific co-chaperone, UNC45. Two UNC45 genes are found in vertebrates, including a striated muscle specific form, Unc45b. We have investigated the role of Unc45b in myosin folding. Epitope tagged murine Unc45b (Unc45bFlag) was expressed in muscle and non-muscle cells and bacteria, isolated and characterized. The protein is a soluble monomer in solution with a compact folded rod-shaped structure of ∼19 nm length by electron microscopy. When over-expressed in striated muscle cells, Unc45bFlag fractionates as a cytosolic protein and isolates as a stable complex with Hsp90. Purified Unc45bFlag re-binds Hsp90 and forms a stable complex in solution. The endogenous Unc45b in muscle cell lysates is also found associated with Hsp90. The Unc45bFlag/Hsp90 complex binds the partially folded myosin motor domain when incubated with myosin subfragments synthesized in a reticulocyte lysate. This binding is independent of the myosin rod or light chains. Unc45bFlag does not bind native myosin subfragments consistent with a chaperone function. More importantly, Unc45bFlag enhances myosin motor domain folding during de novo motor domain synthesis indicating that it has a direct role in myosin maturation. Thus, mammalian Unc45b is a cytosolic protein that forms a stable complex with Hsp90, selectively binds the unfolded conformation of the myosin motor domain, and promotes motor domain folding.
Highlights
Folding of myosin in striated muscle follows a pathway mediated by the molecular chaperones Hsp90, and Hsc70
Folding and assembly of striated muscle myosin is a regulated pathway mediated by molecular chaperones [1,14,16,27,28]
Myosin motor domain folding is assisted in striated muscle cells by the general chaperones Hsp90 and Hsc70 and muscle specific co-factors
Summary
Folding of myosin in striated muscle follows a pathway mediated by the molecular chaperones Hsp, and Hsc. Synthesized myosin forms a transient complex with these general chaperones in which the myosin motor domain is partially folded [1]. Myosin transits through this chaperone complex on the pathway to myofibril assembly. Depletion of Unc45b results in paralysis and cardiac dysfunction in embryos that is correlated with a loss of myosin filaments in sarcomeres. These results are consistent with a role in assembly of muscle specific myosin isoforms required for cranial, cardiac and skeletal muscle contraction [8]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
