BINDING OF A NATIVE TITIN FRAGMENT TO ACTIN IS REGULATED BY PIP2

Titin is a giant protein which extends from Z-line to M-line in striat ed muscles. We report here the purification of a 150-kDa titin fragmen t, obtained after V8 protease treatment of myofibrils, This polypeptid e was located at the N1-line level, in a titin part known to exhibit s tiff properties correlated to an association with actin, By solid or l iquid phase binding assays and cosedimentation, we have clearly demons trated a direct, saturable and relative high affinity binding of the n ative titin fragment to F-actin, The 150-kDa titin fragment was also s hown to accelerate actin polymerization. Furthermore, the actin-titin interaction was found to be inhibited by phosphoinositides. (C) 1998 F ederation of European Biochemical Societies.