Molecular basis of F-actin regulation and sarcomere assembly via myotilin

by Julius Kostan, Miha Pav šič, Vid Puž, Thomas C. Schwarz, Friedel Drepper, Sibylle Molt, Melissa Ann Graewert, Claudia Schreiner, Sara Sajko, Peter F. M. van der Ven, Adekunle Onipe, Dmitri I. Svergun, Bettina Warscheid, Robert Konrat, Dieter O. Fürst, Brigita Lenarčič, Kristina Djinović-Carugo Sarcomeres, the basic contractile units of striated muscle cells, contain arrays of thin (actin) and thick (myosin) filaments that slide past each other during contraction. The Ig-like domain-containing protein myotilin provides structural integrity to Z-discs—the boundaries between adjacent sar comeres. Myotilin binds to Z-disc components, including F-actin and α-actinin-2, but the molecular mechanism of binding and implications of these interactions on Z-disc integrity are still elusive. To illuminate them, we used a combination of small-angle X-ray scattering, cross-linking mass spectro metry, and biochemical and molecular biophysics approaches. We discovered that myotilin displays conformational ensembles in solution. We generated a structural model of the F-actin:myotilin complex that revealed how myotilin interacts with and stabilizes F-actin via its Ig-like domains and flanking regions. Mutant myotilin designed with impaired F-actin binding showed increased dynamics in cells. Structural analyses and competition assays uncovered that myotilin displaces tropomyosin from F-actin. Our findings suggest a novel role of myotilin as a co-organizer of Z-disc assembly and adv...
Source: PLoS Biology: Archived Table of Contents - Category: Biology Authors: Source Type: research