Differential regulation of unconventional fission yeast myosins via the actin track.
BACKGROUND
Fission yeast possesses three unconventional myosins: Myo1p (a class I myosin that functions at endocytic actin patches) and Myo51p and Myo52p (class V myosins that function at contractile rings and actin cables, respectively). Here we used a combination of in vivo and in vitro approaches to investigate how changes in the actin track influence the motor activity and spatial regulation of these myosins.


RESULTS
We optimized the isolation of Myo1p, Myo51p, and Myo52p. All three myosins exhibited robust motor activity in ATPase and actin filament gliding assays. However, decoration of actin with tropomyosin differentially regulates the activity of these motors. Tropomyosin inhibits Myo1p by blocking its ability to form productive associations with actin filaments, whereas tropomyosin increases the actin affinity and ATPase activity of Myo51p and Myo52p. The actin filament crosslinking protein fimbrin rescues Myo1p motor activity by displacing tropomyosin from actin filaments. Consistent with our in vitro findings, fimbrin and tropomyosin have opposing effects on Myo1p function at actin patches. Defects in tropomyosin function led to shorter Myo1p patch lifetimes, whereas loss of fimbrin extended Myo1p lifetimes. Furthermore, defects in tropomyosin function decreased the efficiency of Myo52p-directed motility along actin cables in the cell.


CONCLUSIONS
Tropomyosin promotes myosin-V motility along actin cables. Accumulation of fimbrin at actin patches relieves Myo1p from tropomyosin-mediated inhibition, ensuring maximal myosin-I motor activity at these sites. Thus, spatial regulation of myosin motor function is in part controlled by specific changes in the composition of the actin track.
Clayton
Joseph E
JE
Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA.
Sammons
Matthew R
MR
Stark
Benjamin C
BC
Hodges
Alex R
AR
Lord
Matthew
M
D008841:Actin Cytoskeleton / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism / Q000502:physiology; D004705:Endocytosis / Q000502:physiology; D008562:Membrane Glycoproteins / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism / Q000502:physiology*; D009218:Myosins / Q000378:metabolism / Q000502:physiology*; D021381:Protein Transport / Q000502:physiology; D012568:Schizosaccharomyces / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism / Q000502:physiology*; D014335:Tropomyosin / Q000378:metabolism / Q000502:physiology
C410737:Cdc8 protein, S pombe; D018797:Cell Cycle Proteins; D008562:Membrane Glycoproteins; D008840:Microfilament Proteins; D029702:Schizosaccharomyces pombe Proteins; D014335:Tropomyosin; C491828:myo1 protein, S pombe; C026742:plastin; C554097:Myo52 protein, S pombe; C554096:Myo51 protein, S pombe; D018995:Myosin Heavy Chains; D009218:Myosins