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Published November 2012 | Accepted Version
Journal Article Open

Augmented generation of protein fragments during wakefulness as the molecular cause of sleep: A hypothesis


Despite extensive understanding of sleep regulation, the molecular-level cause and function of sleep are unknown. I suggest that they originate in individual neurons and stem from increased production of protein fragments during wakefulness. These fragments are transient parts of protein complexes in which the fragments were generated. Neuronal Ca^(2+) fluxes are higher during wakefulness than during sleep. Subunits of transmembrane channels and other proteins are cleaved by Ca^(2+)-activated calpains and by other nonprocessive proteases, including caspases and secretases. In the proposed concept, termed the fragment generation (FG) hypothesis, sleep is a state during which the production of fragments is decreased (owing to lower Ca^(2+) transients) while fragment-destroying pathways are upregulated. These changes facilitate the elimination of fragments and the remodeling of protein complexes in which the fragments resided. The FG hypothesis posits that a proteolytic cleavage, which produces two fragments, can have both deleterious effects and fitness-increasing functions. This (previously not considered) dichotomy can explain both the conservation of cleavage sites in proteins and the evolutionary persistence of sleep, because sleep would counteract deleterious aspects of protein fragments. The FG hypothesis leads to new explanations of sleep phenomena, including a longer sleep after sleep deprivation. Studies in the 1970s showed that ethanol-induced sleep in mice can be strikingly prolonged by intracerebroventricular injections of either Ca^(2+) alone or Ca^(2+) and its ionophore. These results, which were never interpreted in connection to protein fragments or the function of sleep, may be accounted for by the FG hypothesis about molecular causation of sleep.

Additional Information

© 2012 The Protein Society. Received 2 August 2012; Accepted 21 August 2012. Published online 28 August 2012. I thank Christopher Brower, Raymond Deshaies, William Dunphy, Konstantin Piatkov, Jevgenij Raskatov, Connor Rosen, Brenda Schulman, Anna Shemorry, and Brandon Wadas for helpful discussions and comments on the manuscript. I am particularly grateful to Roger Kornberg and William Tansey for their detailed suggestions. Our studies of the ubiquitin system and the N-end rule pathway are supported by grants from the National Institutes of Health.

Attached Files

Accepted Version - Varshavsky2012p19367Protein_science_a_publication_of_the_Protein_Society.pdf



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August 22, 2023
October 18, 2023