Dictyostelium myosin 1F and myosin 1E inhibit actin waves in a lipid-binding-dependent and motor-independent manner.

Actin waves are F-actin-rich entities traveling on the ventral plasma membrane by the treadmilling mechanism. Actin waves were first discovered and are best characterized in Dictyostelium. Class I myosins are unconventional monomeric myosins that bind lipids through their tails. Dictyostelium has seven class I myosins, six of these have tails (Myo1A-F) while one has a very short tail (Myo1K), and three of them (Myo1D, Myo1E and Myo1F) bind PIP3 with high affinity. Localization of five Dictyostelium class I myosins synchronizes with localization and propagation of actin waves. Myo1B and Myo1C colocalize with actin in actin waves whereas Myo1D, E and F localize to the PIP3-rich region surrounded by actin waves. Here we studied the effect of overexpression of the three PIP3 specific class I myosins on actin waves. We found that ectopic expression of the short-tail Myo1F inhibits wave formation, short-tail Myo1E has similar but weaker inhibitory effect but long-tail Myo1D does not affect waves. A study of Myo1F mutants shows that its membrane binding site is absolutely required for wave inhibition but the head portion is not. The results suggest that PIP3 specificity and the presence of two membrane binding sites are required for inhibition of actin waves, and that inhibition may be caused by crosslinking of PIP3 heads groups. This article is protected by copyright. All rights reserved.