THE MOLECULAR ELASTICITY OF THE EXTRACELLULAR-MATRIX PROTEIN TENASCIN

Extracellular matrix proteins are thought to provide a rigid mechanica l anchor that supports and guides migrating and rolling cells(1-4). He re we examine the mechanical properties of the extracellular matrix pr otein tenascin by using atomic-force-microscopy techniques. Our result s indicate that tenascin is an elastic protein. Single molecules of te nascin could be stretched to several times their resting length. Force -extension curves showed a saw-tooth pattern, with peaks of force at 1 37 pN. These peaks were similar to 25 nm apart. Similar results have b een obtained by study of titin(5). We also found similar results by st udying recombinant tenascin fragments encompassing the 15 fibronectin type III domains of tenascin. This indicates that the extensibility of tenascin map be due to the stretch-induced unfolding of its fibronect in type III domains. Refolding of tenascin after stretching, observed when the force was reduced to near zero, showed a double-exponential r ecovery with time constants of 42 domains refolded per second and 0.5 domains per second. The former speed of refolding is more than twice a s fast as any previously reported speed of refolding of a fibronectin type III domain(6,7). We suggest that the extensibility of the modular fibronectin type III region may be important in allowing tenascin-lig and bonds to persist over long extensions. These properties of fibrone ctin type III modules may be of widespread use in extracellular protei ns containing such domain(8,9).