A Myosin III from Limulus Eyes Is a Clock-Regulated Phosphoprotein

The lateral eyes of the horseshoe crab Limulus polyphemus undergo dramatic daily changes in structure and function that lead to enhanced retinal sensitivity and responsiveness to light at night. These changes are controlled by a circadian neural input that alters photoreceptor and pigment cell shape...

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Bibliographic Details
Published in:The Journal of neuroscience 1998-06, Vol.18 (12), p.4548-4559
Main Authors: Battelle, Barbara-Anne, Andrews, Anne W, Calman, Bruce G, Sellers, James R, Greenberg, Robert M, Smith, W. Clay
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Animals
Base Sequence
Calmodulin - metabolism
Circadian Rhythm - physiology
DNA, Complementary - genetics
Eye - metabolism
Horseshoe Crabs - metabolism
Immunohistochemistry
Limulus polyphemus
Marine
Molecular Sequence Data
Myosins - genetics
Myosins - metabolism
Phosphoproteins - metabolism
Phosphorylation
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Summary:The lateral eyes of the horseshoe crab Limulus polyphemus undergo dramatic daily changes in structure and function that lead to enhanced retinal sensitivity and responsiveness to light at night. These changes are controlled by a circadian neural input that alters photoreceptor and pigment cell shape, pigment migration, and phototransduction. Clock input to the eyes also regulates photomechanical movements within photoreceptors, including membrane shedding. The biochemical mechanisms underlying these diverse effects of the clock on the retina are unknown, but a major biochemical consequence of activating clock input to the eyes is a rise in the concentration of cAMP in photoreceptors and the phosphorylation of a 122 kDa visual system-specific protein. We have cloned and sequenced cDNA encoding the clock-regulated 122 kDa phosphoprotein and show here that it is a new member of the myosin III family. We report that Limulus myosin III is similar to other unconventional myosins in that it binds to calmodulin in the absence of Ca2+; it is novel in that it is phosphorylated within its myosin globular head, probably by cAMP-dependent protein kinase. The protein is present throughout the photoreceptor, including the region occupied by the photosensitive rhabdom. We propose that the phosphorylation of Limulus myosin III is involved in one or more of the structural and functional changes that occur in Limulus eyes in response to clock input.
ISSN:0270-6474
1529-2401
DOI:10.1523/jneurosci.18-12-04548.1998