Myosin 1s have critical roles in linking membranes to the actin cytoskeleton via direct binding to acidic lipids. Lipid binding may occur through PIP3/PIP2-specific PH domains or nonspecific ionic interactions involving basic-hydrophobic (BH) sites but the mechanism of myosin 1s distinctive lipid targeting is poorly understood. Now we show that PH domains occur in all Dictyostelium myosin 1s and that the BH sites of Myo1A, B, C, D, and F are in conserved positions near the β3/β4 loops of their PH domains. In spite of these shared lipid-binding sites, we observe significant differences in myosin 1s highly dynamic localizations. All myosin 1s except Myo1A are present in macropinocytic structures but only Myo1B and Myo1C are enriched at the edges of macropinocytic cups and associate with the actin in actin waves. In contrast, Myo1D, E, and F are enclosed by the actin wave. Mutations of BH sites affect localization of all Dictyostelium myosin 1s. Notably, mutation of the BH site located within the PH domains of PIP3-specific Myo1D and Myo1F completely eradicates membrane binding. Thus, BH sites are important determinants of motor targeting and may have a similar role in the localization of other myosin 1s.
Bibliographical noteFunding Information:
We acknowledge the support of the Light Microscopy Core of the Intramural Research Program of the National Heart, Lung, and Blood Institute. We thank Livia Songster for help with transformations and the initial screen of expressed proteins and Michael Bag-noli for help with cell culturing and data processing. This work was supported by the Intramural Research Program of the National Heart, Lung, and Blood Institute and by National Institutes of Health Grant no. R01GM-122917 to M.A.T. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
© 2020 Brzeska et al.