SignificanceClass II myosins are the only members of this superfamily of actin-associated molecular motors that form antiparallel bipolar filaments, which are essential for the biological functions of these myosins. Here we show that the assembly of Acanthamoeba myosin II monomers into minifilaments is modified by phosphorylation of one or more of four serine residues in the 27-residue nonhelical tailpiece at the end of each of the two heavy chains that form the coiled-coil helix characteristic of class II myosins. This regulatory mechanism might be applicable to other class II myosins that have a nonhelical tailpiece.
[Show abstract][Hide abstract] ABSTRACT: SignificanceMyosin II from the soil amoeba Acanthamoeba castellanii is a member of the largest of the 35 classes of the superfamily of molecular motors that, together with actin filaments, convert the energy of hydrolysis of ATP into force or motion that drives numerous cellular and intracellular processes. In this paper we show that the actin-activated ATPase of Acanthamoeba myosin II is regulated by phosphorylation of a specific serine in a region of the myosin motor domain that is known to be at the myosin-actin interface. No other myosin has been shown to be regulated in this way.
Proceedings of the National Academy of Sciences 12/2012; 110(1). DOI:10.1073/pnas.1219713110 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Phosphorylation of S639 in loop-2 of the catalytic motor domain of the heavy chain of Acanthamoeba castellanii myosin-2 and the phosphomimetic mutation S639D have been shown previously to down-regulate the actin-activated ATPase activity of both the full-length myosin and single-headed subfragment-1 (Liu et al. (2013) Proc. Natl. Acad. Sci. USA 110, E23-32). In the present study we determined the kinetic constants for each step in the myosin and actomyosin ATPase cycles of recombinant wild-type S1 and S1-S639D. The kinetic parameter predominantly affected by the S639D mutation is the actin-activated release of inorganic phosphate from the myosin•ADP•Pi complex, which is the rate-limiting step in the steady-state actomyosin ATPase cycle. As consequence of this change, the duty ratio of this conventional myosin decreases. We speculate on the effect of S639 phosphorylation on the processive behavior of myosin-2 filaments.
[Show abstract][Hide abstract] ABSTRACT: Class XIVa myosins are a unique group of myosin motor proteins found in apicomplexan parasites, including those that cause malaria and toxoplasmosis. The founding member of the class XIVa family, Toxoplasma gondii myosin A (TgMyoA), is a monomeric unconventional myosin that functions at the parasite periphery to control gliding motility, host cell invasion and host cell egress. How the motor activity of TgMyoA is regulated during these critical steps in the parasite's lytic cycle is unknown. We show here that a small-molecule enhancer of T. gondii motility and invasion (compound 130038) causes an increase parasite intracellular calcium levels leading to a calcium-dependent increase in TgMyoA phosphorylation. Mutation of the major sites of phosphorylation altered parasite motile behavior upon compound 130038 treatment, and parasites expressing a non-phosphorylatable mutant myosin egressed from host cells more slowly in response to treatment with calcium ionophore. These data demonstrate that TgMyoA undergoes calcium-dependent phosphorylation, which modulates myosin-driven processes in this important human pathogen.
Molecular Biology of the Cell 07/2014; 25(17). DOI:10.1091/mbc.E13-11-0648 · 4.47 Impact Factor
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