The actin-binding interface of a myosin III is phosphorylated in vivo in response to signals from a circadian clock.
Class III unconventional myosins are critical for the normal function of auditory hair cells and the function and maintenance of photoreceptors; however, the roles of class III myosins in these sensory cells are unknown. Class III myosins are unique in that they have a kinase domain at their N-terminus; thus, they may have both signaling and motor functions. In the horseshoe crab Limulus polyphemus, enhanced phosphorylation of an abundant, photoreceptor specific class III myosin at night correlates with well-characterized circadian changes in photoreceptor structure and function. Thus, the Limulus visual system may be particularly useful for investigating the properties, modulation, and functions of a class III myosin. Previously, we showed that two sites within the actin interface of full-length Limulus myosin III expressed in baculovirus are substrates for both cyclic AMP-dependent protein kinase and autophosphorylation. In the current study, mass spectrometry was used to show that these same sites are phosphorylated in the endogenous protein extracted from Limulus lateral eye, and that enhanced phosphorylation at these sites occurs in vivo in response to natural circadian clock input to these eyes. These findings demonstrate in vivo changes in myosin III phosphorylation in response to a natural stimulus. This phosphorylation may modulate myosin III-actin interactions.
Cardasis
Helene L
HL
Department of Chemistry, University of Florida, Gainesville, Florida 32611, USA.
Stevens
Stanley M
SM
McClung
Scott
S
Kempler
Karen E
KE
Powell
David H
DH
Eyler
John R
JR
Battelle
Barbara-Anne
BA
D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001683:Biological Clocks; D002853:Chromatography, Liquid; D002940:Circadian Rhythm; D006737:Horseshoe Crabs; D008969:Molecular Sequence Data; D025102:Myosin Type III / Q000378:metabolism*; D010766:Phosphorylation; D015398:Signal Transduction; D053719:Tandem Mass Spectrometry
D000199:Actins; D025102:Myosin Type III