TEDs Site Phosphorylation Regulates Myosin I Motor Activity And Function In Fission Yeast

Abstract

Myosins are evolutionarily conserved motor proteins that associate with actin to undertake a plethora of diverse cellular functions. Type I myosins are single headed monomeric motors which are involved in a range of motile and sensory activities in a variety of cell types. Myosin I's from lower eukaryotes have a conserved “TEDs site” motif within its motor domain. Phosphorylation of a conserved serine residue within this motif plays an important role in regulating the motor protein's activity. However, the mechanism by which TEDs site phosphorylation affects the motor activity and function of each myosin I remains unclear.The sole class I myosin in the fission yeast, Schizosaccharomyces pombe, Myo1 is required to promote polymerisation of cortical actin patches, as well as to regulate lipid organisation and endocytosis. We have identified the serine residue within the motor domain of Myo1, which corresponds to the TEDs site. Using a phosphospecific antibody we have established that this conserved serine is phosphorylated in vivo within fission yeast. Mutating this serine within the Myo1 protein to either alanine or aspartic acid has revealed that its normal phosphorylation plays a crucial role in regulating the protein's affinity for actin and ability to function within the cell. Live cell imaging of these strains indicate Myo1 TEDs site phosphorylation is required for Myo1 to recruit to dynamic non-motile foci at the cell surface. In addition and unregulated phosphorylation can lead to inappropriate association with actin filaments, which is normally inhibited by tropomyosin. We also present data which illustrate the important role this phosphorylation event plays in Myo1's functions during actin organisation, endocytosis and lipid raft distribution.