Structural Determinants for the Intracellular Degradation of Human Thymidylate Synthase

Forsthoefel, Antonia M.; Peña, Maria Marjorette O.; Xing, Yang; Rafique, Zubaid; Berger, Franklin G.

doi:10.1021/bi035894p

Cited by 44 publications

(64 citation statements)

References 42 publications

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“…In eukaryotes too some proteins are targeted to the proteasome directly by sequence motifs in their primary structure [59,60]. Degradation of thymidylate synthase (TS) and ornithine decarboxylase (ODC) by the proteasome is mediated by specific sequences, at the N terminus for TS and at the C terminus for ODC, and does not depend on ubiquitin [59,60].…”

Section: Targeting Signals In the Primary Sequence Of The Substratesmentioning

confidence: 99%

“…Degradation of thymidylate synthase (TS) and ornithine decarboxylase (ODC) by the proteasome is mediated by specific sequences, at the N terminus for TS and at the C terminus for ODC, and does not depend on ubiquitin [59,60]. These degradation signals also serve as both the protease binding site and the degradation initiation site.…”

Section: Targeting Signals In the Primary Sequence Of The Substratesmentioning

confidence: 99%

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Protein targeting to ATP-dependent proteases

Inobe

Matouschek

2008

Current Opinion in Structural Biology

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ATP-dependent proteases control diverse cellular processes by degrading specific regulatory proteins. Understanding how these regulatory proteins are targeted to ATP-dependent proteases is of central importance to understanding their biological role as regulators. Recent work has shown that protein substrates are specifically transferred to ATP-dependent proteases through different routes. These routes can function in parallel or independently. In all of these targeting mechanisms it can be useful to separate two steps: substrate binding to the protease and initiation of degradation.To be active, newly synthesized protein chains must fold into three-dimensional structures, but regulated unfolding is also critically important in some biological processes, such as protein degradation by ATP-dependent proteases and protein translocation across membranes [1]. Unfolding is required during degradation because the proteolytic sites of the ATP-dependent proteases are sequestered deep inside the proteases' structures and accessible only through narrow openings. Similarly, unfolding is required during several translocation processes because the protein import channels in some organelles are not wide enough for native proteins to fit through them. The mechanisms of unfolding in both types of processes are similar to each other but different from that of unfolding induced by heat or chemical denaturants. Here we discuss how the requirement for protein unfolding during degradation affects the way ATPdependent proteases select their substrates. ATP-dependent proteasesATP-dependent proteases degrade short-lived regulatory proteins and thereby control cellular processes such as signal transduction, cell cycle, and gene transcription. The proteases also clear misfolded and aggregated proteins from the cell and produce some of the peptides to be displayed at cell surface as part of adaptive immune response. In eukaryotes, these functions are performed mainly by the proteasome. In prokaryotes and the organelles of eukaryotes, the functions are fulfill by analogues of the proteasome, such as the ClpAP, ClpXP, HslUV, FtsH, and Lon proteases. Although ATP-dependent proteases show only relatively little sequence identity, they share a common architecture [2].The ATP-dependent proteases all form large multisubunit particles (Figure 1). In the simplest case, FtsH protease, the particle consists 6 copies of a 71 kDa subunit forming a complex of approximately 425 kDa, and in the most complex case, the proteasome, the particle consists of some 40 different subunits forming a complex of 2 MDa molecular weight [3,4]. The subunits are mostly arranged in six or seven subunit rings that stack on top of each other to

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Section: Targeting Signals In the Primary Sequence Of The Substratesmentioning

confidence: 99%

Section: Targeting Signals In the Primary Sequence Of The Substratesmentioning

confidence: 99%

Protein targeting to ATP-dependent proteases

Inobe

Matouschek

2008

Current Opinion in Structural Biology

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“…Although we cannot completely rule out the possibility that Alg13p is ubiquitinated for proteasomal degradation, our data in Figure 4 show that ubiquitination does not enhance Alg13p degradation (Figure 4). Thus, like ODC and human thymidylate synthase, which are exclusively degraded independently of ubiquitin (Bercovich et al, 1989;Gandre et al, 2003;Forsthoefel et al, 2004), Alg13p may represent another rare example of a protein whose proteasomal degradation does not involve ubiquitin at all.…”

Section: Alg13p Is Degraded By the Proteasome But Does Not Require Ubmentioning

confidence: 99%

Alg13p, the Catalytic Subunit of the Endoplasmic Reticulum UDP-GlcNAc Glycosyltransferase, Is a Target for Proteasomal Degradation

Averbeck

Gao

Nishimura

et al. 2008

MBoC

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The second step of dolichol-linked oligosaccharide synthesis in the N-linked glycosylation pathway at the endoplasmic reticulum (ER) membrane is catalyzed by an unusual hetero-oligomeric UDP-N-acetylglucosamine transferase that in most eukaryotes is comprised of at least two subunits, Alg13p and Alg14p. Alg13p is the cytosolic and catalytic subunit that is recruited to the ER by the membrane protein Alg14p. We show that in Saccharomyces cerevisiae, cytosolic Alg13p is very short-lived, whereas membrane-associated Alg13 is relatively stable. Cytosolic Alg13p is a target for proteasomal degradation, and the failure to degrade excess Alg13p leads to glycosylation defects. Alg13p degradation does not require ubiquitin but instead, requires a C-terminal domain whose deletion results in Alg13p stability. Conversely, appending this sequence onto normally long-lived ␤-galactosidase causes it to undergo rapid degradation, demonstrating that this C-terminal domain represents a novel and autonomous degradation motif. These data lead to the model that proteasomal degradation of excess unassembled Alg13p is an important quality control mechanism that ensures proper protein complex assembly and correct N-linked glycosylation.

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“…25 Degradation of the TS polypeptide has recently been shown to be mediated by the 26S proteasome in a ubiquitin-independent manner, with the N-terminal end of the protein, which is unstructured and extended in the mammalian enzyme, playing a prominent role. 26 Regardless of mechanism, elevation in TS concentration upon the binding of inhibitory ligands may be a limiting factor in the clinical response to TS inhibitors.…”

Section: Thymidylate Synthase As a Chemotherapeutic Drug Targetmentioning

confidence: 99%