An unexpectedly large working stroke from chymotryptic fragments of myosinII

Recent structural evidence indicates that the light chain domain of the myo sin head (LCD) bends on the motor domain (MD) to move actin. Structural mod els usually assume that the actin-MD interface remains static and the possi bility that part of the myosin working stroke might be produced by rotation about the acto-myosin interface has been neglected. We have used an optica l trap to measure the movement produced by proteolytically shortened single rabbit skeletal muscle myosin heads (S-1(A1) and S-1(A2)), The working str oke produced by these shortened heads was more than that which the MD-LCD b end mechanism predicts from the full-length (papain) S-1's working stroke o btained under similar conditions, This result indicates that part of the wo rking stroke may be caused by motor action at the actin-MD interface. (C) 2 000 Federation of European Biochemical Societies. Published by Elsevier Sci ence B.V. All rights reserved.