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Augmented generation of protein fragments during wakefulness as the molecular cause of sleep: a hypothesis
Author(s) -
Varshavsky Alexander
Publication year - 2012
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.2148
Subject(s) - calpain , wakefulness , sleep (system call) , sleep deprivation , transmembrane protein , neuroscience , proteolysis , chemistry , proteases , microbiology and biotechnology , biochemistry , endocrinology , biology , medicine , circadian rhythm , enzyme , receptor , electroencephalography , computer science , operating system
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 (Erickson et al. , Science 1978;199:1219–1221; Harris, Pharmacol Biochem Behav 1979;10:527–534; Erickson et al. , Pharmacol Biochem Behav 1980;12:651–656). 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.