Abstract
Class I myosins are single-headed motor proteins, implicated in various motile processes including organelle translocation, ion-channel gating, and cytoskeleton reorganization. Here we describe the cellular localization of myosin-IE and its role in the phagocytic uptake of solid particles and cells. A complete analysis of the kinetic and motor properties of Dictyostelium discoideum myosin-IE was achieved by the use of motor domain constructs with artificial lever arms. Class I myosins belonging to subclass IC like myosin-IE are thought to be tuned for tension maintenance or stress sensing. In contrast to this prediction, our results show myosin-IE to be a fast motor. Myosin-IE motor activity is regulated by myosin heavy chain phosphorylation, which increases the coupling efficiency between the actin and nucleotide binding sites tenfold and the motile activity more than fivefold. Changes in the level of free Mg(2+) ions, which are within the physiological range, are shown to modulate the motor activity of myosin-IE by inhibiting the release of adenosine diphosphate.
Highlights
Myosins form a large family of mechano-enzymes that contain a common domain by which they bind to actin and convert the energy from the hydrolysis of ATP into movement along actin filaments
A complete analysis of the kinetic and motor properties of Dictyostelium discoideum myosin-IE was achieved by the use of motor domain constructs with artificial lever arms
Myosin-IE motor activity is regulated by myosin heavy chain phosphorylation, which increases the coupling efficiency between the actin and nucleotide binding sites tenfold and the motile activity more than fivefold
Summary
Myosins form a large family of mechano-enzymes that contain a common domain by which they bind to actin and convert the energy from the hydrolysis of ATP into movement along actin filaments. On the basis of sequence comparisons of their highly conserved catalytic domain, members of the myosin family have been grouped into 18 classes (Berg et al, 2001). Among the most prevalent and most widely expressed myosins are the monomeric, non-filamentous class I myosins. The conserved N-terminal motor domain of class I myosins, which contains the ATP- and actin-binding sites, is followed by one to six light-chain-binding IQ-motifs and more diverse C-terminal tail regions. We describe the functional properties of Dictyostelium discoideum myosin-IE, a member of the short-tailed myosin-I␣ subfamily. We have solved the crystal structure of the myosinIE motor domain and described the basic kinetic properties of a motor domain construct (Kollmar et al, 2002)
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