The N-end rule pathway for regulated proteolysis: prokaryotic and eukaryotic strategies

Mogk, Axel; Schmidt, Ronny; Bukau, Bernd

doi:10.1016/j.tcb.2007.02.001

Cited by 232 publications

(241 citation statements)

References 37 publications

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“…2 D and E). No peptides containing N-terminal methionine were detected, suggesting that translation initiation in cells occurs without incorporating an N-terminal methionine or that it is removed rapidly by methionine aminopeptidase or endopeptidase activity (12). Additionally, the predicted C-terminal digestion fragment (TTTT-SSYPYDVPDYA) was identified (Fig.…”

Section: Resultsmentioning

confidence: 99%

Non-ATG–initiated translation directed by microsatellite expansions

Zu¹,

Gibbens²,

Doty³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

785

1,022

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Trinucleotide expansions cause disease by both protein-and RNAmediated mechanisms. Unexpectedly, we discovered that CAG expansion constructs express homopolymeric polyglutamine, polyalanine, and polyserine proteins in the absence of an ATG start codon. This repeat-associated non-ATG translation (RAN translation) occurs across long, hairpin-forming repeats in transfected cells or when expansion constructs are integrated into the genome in lentiviral-transduced cells and brains. Additionally, we show that RAN translation across human spinocerebellar ataxia type 8 (SCA8) and myotonic dystrophy type 1 (DM1) CAG expansion transcripts results in the accumulation of SCA8 polyalanine and DM1 polyglutamine expansion proteins in previously established SCA8 and DM1 mouse models and human tissue. These results have implications for understanding fundamental mechanisms of gene expression. Moreover, these toxic, unexpected, homopolymeric proteins now should be considered in pathogenic models of microsatellite disorders.T ranslation of mRNA into protein is an exquisitely regulated, almost error-free process. Well-established rules of translational initiation have been used as a cornerstone in biology to understand gene expression and to predict the consequences of disease-causing mutations (1). For microsatellite expansion disorders, mutations within or outside ATG-initiated ORFs are thought to cause disease either by protein gain-of-function, protein loss-of-function, or RNA gain-of-function mechanisms (2, 3).Microsatellite expansion mutations that express polyglutamine (polyGln) expansion proteins include Huntington disease (Huntingtin, HD), spinal bulbar muscular atrophy, and spinocerebellar ataxia types 1, 2, 3, 6, 7, and 17. Since the discovery of these CAG·CTG expansion mutations, efforts to understand disease mechanisms have focused on elucidating the molecular effects of the polyGln proteins expressed from these loci. Although these polyGln expansion proteins bear no similarity to each other apart from the polyGln tract, a hallmark of these diseases is protein accumulation and aggregation in nuclear or cytoplasmic inclusions. Surprisingly, although the polyGln expansion proteins are widely expressed in the CNS and other tissues, only restricted populations of neurons are vulnerable in each disease (3).Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are the best-characterized examples of RNA-mediated expansion disorders (2). The mutation causing DM1 is a CTG-repeat expansion located in the 3′ UTR of the dystrophia myotonica-protein kinase (DMPK) gene. Although DM1 can be clinically more severe than DM2, the discovery of the DM2 mutation and several mouse models provide strong support that many features of these diseases result from RNA gain-of-function effects in which the dysregulation of RNA-binding proteins is mediated by the expression of CUG and CCUG transcripts (4). Additionally, RNA gain-of-function effects have been reported for CGG and CAG expansion RNAs (5, 6).Both RNA and protein mechanisms appear to operate...

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Section: Resultsmentioning

confidence: 99%

Non-ATG–initiated translation directed by microsatellite expansions

Zu¹,

Gibbens²,

Doty³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

785

1,022

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“…The N-end rule pathway consists of two branches, the Ac/N-end rule and the Arg/N-end rule pathways (for reviews, see Refs. 122,124,128,129,239). The Ac/N-end rule pathway, described below, recognizes proteins with Ntacetylated N-terminal residues.…”

Section: Fragments Of Neuronal Proteins As N-end Rule Substratesmentioning

confidence: 99%

“…Just two examples of the likely relevance of FG concepts outside sleep-muscle fatigue and mechanisms of memory-are briefly mentioned below, but many such settings may exist in all organisms, including prokaryotes, which contain both nonprocessive proteases and specific versions of the N-end rule pathway. 122,129,266,267 The roles of calpains in mammalian cells of different types are broadly similar to calpain functions in neurons. In myotubes of the skeletal muscle and in cardiomyocytes of the heart, calpains can cleave cytoskeletal proteins such as cortactin, vimentin, dystrophin, talin, troponin, actin, and titin [ Fig.…”

Section: The Fg Hypothesis and Settings Other Than Sleepmentioning

confidence: 99%

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

Varshavsky

2012

Protein Science

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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 21 fluxes are higher during wakefulness than during sleep. Subunits of transmembrane channels and other proteins are cleaved by Ca 21 -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 21 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 21 alone or Ca 21 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.

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“…R egulated intracellular proteolysis is crucial in many physiological processes, including the elimination of misfolded or truncated proteins, the initiation of appropriate transcriptional responses to cellular stress, and the control of protein life span (1)(2)(3)(4). In organisms ranging from bacteria to mammals, intracellular degradation is frequently catalyzed by multisubunit AAAϩ proteolytic machines.…”

mentioning

confidence: 99%

“…The critical step in degradation is recognition. In bacteria, AAAϩ proteases recognize appropriate substrates via short accessible peptide sequences, called degradation tags or degrons (4,5). After binding, the protease uses repetitive cycles of ATP hydrolysis to unfold the substrate and then to translocate the denatured polypeptide into a sequestered chamber for degradation.…”

mentioning

confidence: 99%

Molecular basis of substrate selection by the N-end rule adaptor protein ClpS

Roman-Hernandez¹,

Grant²,

Sauer³

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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The N-end rule is a conserved degradation pathway that relates the stability of a protein to its N-terminal amino acid. Here, we present crystal structures of ClpS, the bacterial N-end rule adaptor, alone and engaged with peptides containing N-terminal phenylalanine, leucine, and tryptophan. These structures, together with a previous structure of ClpS bound to an N-terminal tyrosine, illustrate the molecular basis of recognition of the complete set of primary N-end rule amino acids. In each case, the ␣-amino group and side chain of the N-terminal residue are the major determinants of recognition. The binding pocket for the N-end residue is preformed in the free adaptor, and only small adjustments are needed to accommodate N-end rule residues having substantially different sizes and shapes. M53A ClpS is known to mediate degradation of an expanded repertoire of substrates, including those with N-terminal valine or isoleucine. A structure of Met53A ClpS engaged with an N-end rule tryptophan reveals an essentially wild-type mechanism of recognition, indicating that the Met 53 side chain directly enforces specificity by clashing with and excluding ␤-branched side chains. Finally, experimental and structural data suggest mechanisms that make proteins with N-terminal methionine bind very poorly to ClpS, explaining why these high-abundance proteins are not degraded via the N-end rule pathway in the cell.AAAϩ ATPase adaptor ͉ clpAP protease ͉ degradation tag ͉ degron

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The N-end rule pathway for regulated proteolysis: prokaryotic and eukaryotic strategies

Cited by 232 publications

References 37 publications

Non-ATG–initiated translation directed by microsatellite expansions

Non-ATG–initiated translation directed by microsatellite expansions

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

Molecular basis of substrate selection by the N-end rule adaptor protein ClpS

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