( rdered making them easier to study str...)Spiders help scientists discover how muscles relax

Padron and Lorenzo Alamo at IVIC partnered with Roger Craig, John Woodhead and Fa-Qing Zhao at the University of Massachusetts Medical School to use cryo-electron microscopy to answer questions about the thick filament's structure, questions that could not be answered with existing electron microscopy techniques.

Standard electron microscopy requires dehydration and staining of a tissue sample, which modifies the structure of the specimen and distorts its shape. Cryo-electron microscopy avoids these problems by rapidly freezing the sample. Using the new technique, the researchers were able to visualize the muscle tissue in a form closer to its structure in the body than had previously been possible. It took several years to refine the techniques required to preserve the thick muscle filaments in their relaxed state. Even then, the researchers faced mathematical difficulties in calculating a three-dimensional map of the filaments. In 2004, using a new approach that Edward Egelman at the University of Virginia Health Sciences Center had developed to create the map, they soon had their structure. "The new reconstruction was very detailed; we were all amazed with the level of detail that it showed," Padron said.

The structure provides crucial new details. A twisting, symmetrical arrangement of myosin heads spaced around the filament's circumference surrounds a backbone made up of 12 parallel strands or sub-filaments. "This is the first time that the structure of the backbone has been clearly seen in any thick filament reconstruction," the researchers wrote.

"The structure reveals how the helices of the myosin heads are formed and maintained and how the filaments are switched off due to interactions between the myosin heads Padron explained. "It also opens the way to understanding how the thick fi
'"/>

Source:Howard Hughes Medical Institute