The coding sequence for the adult myosin heavy chain (MyHC) isoforms is among the most heavily amplified in mammalian species, including humans. The resulting polypeptide generally accounts for 15-25% of the total body protein, and the large size of the 17p13.1 locus with the MyHC genes would predict a prominent role for MyHC mutations in human myopathy. However, a large proportion of patients evaluated for skeletal muscle weakness still fail to receive specific diagnosis and there is accordingly a significant need to improve molecular diagnostic tools together with structure-function analyzes of the motor protein myosin. By combining cell- and molecularphysiological techniques with sensitive protein separation and quantification methods, electrophysiological, molecular biological and structural analyses we have a unique opportunity to unravel the mechanisms underlying the motor handicap associated primary and secondary myopathies affecting the molecular motor protein myosin and other sarcomeric proteins. The overall goal of our research is to have a detailed understanding of how muscle contraction is regulated by myofibrillar proteins at the cellular and molecular levels, and to transfer this information from basic science into practical clinical knowledge in muscle disorders affecting myosin. The specific aims of this project are to: (1) Develop or modify methods to study myosin expression, structure and function, design diagnostic methods, and implement relevant experimental animal models, and (2) Unravel the mechanisms underlying the motor handicap associated with acquired and hereditary myosinopathies. Specific interest will be focused on the acquired myosin loss and muscle paralysis in ICU patients and the hereditary myopathies caused by missense mutations of different sarcomeric proteins.