Ste20-kinase-dependent TEDS-site phosphorylation modulates the dynamic localisation and endocytic function of the fission yeast class I myosin, Myo1

Abstract

Type I myosins are monomeric motors involved in a range of motile and sensory activities in different cell types. In simple unicellular eukaryotes, motor activity of class I myosins is regulated by phosphorylation of a conserved `TEDS site' residue within the motor domain. The mechanism by which this phosphorylation event affects the cellular function of each myosin I remains unclear. The fission yeast myosin I, Myo1, activates Arp2/3-dependent polymerisation of cortical actin patches and also regulates endocytosis. Using mutants and Myo1-specific antibodies, we show that the phosphorylation of the Myo1 TEDS site (serine 361) plays a crucial role in regulating this protein's dynamic localisation and cellular function. We conclude that although phosphorylation of serine 361 does not affect the ability of this motor protein to promote actin polymerisation, it is required for Myo1 to recruit to sites of endocytosis and function during this process.

The recruitment of acetylated and unacetylated tropomyosin to distinct actin polymers permits the discrete regulation of specific myosins in fission yeast

“…Consistent with these observations we discovered that myosin V and myosin I movement are unaffected by lack of Tm acetylation. Although Myo1 normally only associates with short polymers of cortical actin, and is prevented from associating with actin filaments labelled with forms of Cdc8 (Attanapola et al, 2009;Sirotkin et al, 2005), Tm acetylation has no effect upon this inhibition. Similarly our findings show that Myo52 motility not being affected by Cdc8 acetylation is consistent with the observations that Tm does not affect the motility of mammalian myosin Va in vitro (Stark et al, 2010).…”

“…The fission yeast class I myosin, Myo1, localises to dynamic foci at sites of cell growth, from which they seed the polymerisation of Arp2/3-dependent actin patches and promote endocytosis (Attanapola et al, 2009;Codlin et al, 2008;Lee et al, 2000). As these actin structures lack Cdc8 it was unsurprising that lack of Tm acetylation had no significant affect upon the cellular distribution of this motor protein, which continued to be recruited to foci at sites of growth in naa25 cells (Fig.…”

A calmodulin-related light chain from fission yeast that functions with myosin-I and PI 4-kinase

“…Myo1p function is required for maintenance of cell polarity, sporulation and organization of sterol-rich domains at the plasma membrane (Lee et al, 2000;Takeda and Chang, 2005;Toya et al, 2001). Myosin-I motor activity promotes internalization of endocytic vesicles in both budding and fission yeast (Attanapola et al, 2009;Sun et al, 2006). Unlike long-tailed myosins in other species, yeast myosin-I tails possess a C-terminal acidic domain that contributes to activation of the Arp2/3 complex (Evangelista et al, 2000;Lechler et al, 2000;Lee et al, 2000).…”

Regulation and function of the fission yeast myosins

“…This Myo1 function is reflected in the phenotype of myo1⌬ cells, which lack a polarised distribution of cortical actin patches as well as a polarised pattern of cell growth. Similarly, Myo1 associates with actin patches (Lee et al, 2000;Sirotkin et al, 2005;Toya et al, 2001), where it not only promotes actin polymerisation but also plays a key role in membrane remodelling and endocytosis (Attanapola et al, 2009;Codlin et al, 2008). Its association with the membrane is highly dynamic; each interaction lasts ~14 seconds.…”

“…Its association with the membrane is highly dynamic; each interaction lasts ~14 seconds. However, no substantial lateral Myo1 movements have been observed, indicating that it does not travel along actin cables during (Attanapola et al, 2009;Sirotkin et al, 2005;Takeda and Chang, 2005). As in all class I myosins, the tail of Myo1 contains a conserved tail homology domain (TH1 domain), which is required for the association of Myo1 with dynamic lipid regions.…”