Using muscle tissue from tarantulas, an HHMI international research scholar and his colleagues have figured out the detailed structure and arrangement of the miniature molecular motors that control movement. Their work, which takes advantage of a new technique for visualizing tissues in their natural state, provides new insights into the molecular basis of muscle relaxation, and perhaps its activation too.

"We have solved the structure of the array of miniature motors that form our muscles and found out how they are switched off," said Ral Padrn, a HHMI international research scholar in the Department of Structural Biology at the Venezuelan Institute for Scientific Research (Instituto Venezolano de Investigaciones Cientficas or IVIC) in Caracas, Venezuela.

The findings are reported in the August 25, 2005, issue of the journal Nature.

Padrn and his colleagues focused their studies on striated muscle--the type of muscle that controls skeletal movement and contractions of the heart. Striated muscles are made of long cylindrical cells called muscle fibers. Within the fibers, millions of units known as sarcomeres give rise to movement of skeletal muscles. Sarcomeres are composed mainly of thick filaments of myosin, the most common protein in muscle cells, responsible for their elastic and contractile properties. The thick filaments are arranged in parallel with thin filaments of another muscle protein, actin. When the actin and myosin filaments slide along one another, the muscle contracts or relaxes.

Padrn's study focused on the long, rod-shaped myosin of the thick filaments. The heads of these myosin rods project outward from the thick filament to connect with and move actin filaments during contraction of a muscle.

The structural studies were done using tarantula striated muscle, which the team has been studying since the 1980s. Striated muscles from the large, hairy spiders contain filaments that are particularly well order
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Contact: Jennifer Donovan
donovanj@hhmi.org
301-215-8859
Howard Hughes Medical Institute
24-Aug-2005

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