Projectin and kettin are titin-like proteins mainly responsible for the high passive stiffness of insect indirect flight muscles, which is needed to generate oscillatory work during flight. Here we report the mechanical properties of kettin and projectin by single-molecule force spectroscopy. Force-extension and force-clamp curves obtained from Lethocerus projectin and Drosophila recombinant projectin or kettin fragments revealed that fibronectin type III domains in projectin are mechanically weaker (unfolding force, F u ≈ 50-150 pN) than Ig-domains (Fu ≈ 150-250 pN). Among Ig domains in Sls/kettin, the domains near the N terminus are less stable than those near the C terminus. Projectin domains refolded very fast [85% at 15 s-1 (25°C)] and even under high forces (15-30 pN). Temperature affected the unfolding forces with a Q10 of 1.3, whereas the refolding speed had a Q10 of 2-3, probably reflecting the cooperative nature of the folding mechanism. High bending rigidities of projectin and kettin indicated that straightening the proteins requires low forces. Our results suggest that titin-like proteins in indirect flight muscles could function according to a folding-based-spring mechanism.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Mar 21 2006|
- Force spectroscopy
- Single molecule
ASJC Scopus subject areas