The effect of the <scp>L</scp>‐azetidine‐2‐carboxylic acid residue on protein conformation. I. Conformations of the residue and of dipeptides

Zagari, Adriana; Némethy, George; Scheraga, Harold A.

doi:10.1002/bip.360300909

Cited by 49 publications

(31 citation statements)

References 28 publications

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“…However, since translation is required for homoserine toxicity, homoserine may be misacylated by multiple aminoacyl tRNA synthetases, as is the case for homocysteine (12,13,(41)(42)(43)(44). Various homoserinemediated deleterious phenotypes observed for thr1⌬ and thr4⌬ mutants would be consistent with homoserine incorporation into proteins, creating aberrant proteins that are sensitive to various stresses, analogous to effects mediated by the incorporation into protein of toxic amino acid analogs (93,96). If homoserine is incorporated into proteins causing misfolding, this would also be consistent with thr1⌬ and thr4⌬ being synthetic lethal with hsp82⌬, an isoform of the chaperone HSP90 important for protein folding (68), and/or having increased sensitivity to HSP90 inhibitors (57,97).…”

Section: Discussionmentioning

confidence: 91%

Homoserine Toxicity in Saccharomyces cerevisiae and Candida albicans Homoserine Kinase ( thr1 Δ) Mutants

Kingsbury

McCusker

2010

Eukaryot Cell

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In addition to threonine auxotrophy, mutation of the Saccharomyces cerevisiae threonine biosynthetic genes THR1 (encoding homoserine kinase) and THR4 (encoding threonine synthase) results in a plethora of other phenotypes. We investigated the basis for these other phenotypes and found that they are dependent on the toxic biosynthetic intermediate homoserine. Moreover, homoserine is also toxic for Candida albicans thr1⌬ mutants. Since increasing levels of threonine, but not other amino acids, overcome the homoserine toxicity of thr1⌬ mutants, homoserine may act as a toxic threonine analog. Homoserine-mediated lethality of thr1⌬ mutants is blocked by cycloheximide, consistent with a role for protein synthesis in this lethality. We identified various proteasome and ubiquitin pathway components that either when mutated or present in high copy numbers suppressed the thr1⌬ mutant homoserine toxicity. Since the doa4⌬ and proteasome mutants identified have reduced ubiquitin-and/or proteasome-mediated proteolysis, the degradation of a particular protein or subset of proteins likely contributes to homoserine toxicity.The enzymatic reactions and regulation of the threonine biosynthetic pathway, which have attracted interest as a set of potential antifungal drug targets (11,(48)(49)(50), have been studied extensively in the yeast Saccharomyces cerevisiae (46). Yeast synthesizes threonine from aspartate in five enzymatic steps via the intermediate homoserine, which is also required for methionine synthesis ( Fig. 1) (reviewed in reference 46). Homoserine is converted to threonine by the sequential actions of homoserine kinase (Thr1p) and threonine synthase (Thr4p). The threonine pathway is regulated at various steps. A majority of the pathway genes are regulated at the transcriptional level by general control in response to amino acid starvation (34, 64). The pathway is also regulated at the level of enzyme activity, most critically by threonine feedback inhibition of aspartate kinase (Hom3p), the initial step of the pathway (56, 73), which requires an interaction between Hom3p and the FPR1-encoded FK506-binding protein, FKBP12 (1).In addition to threonine auxotrophy, a number of phenotypes have been observed in homoserine kinase (thr1) and/or threonine synthase (thr4) mutants, including being petite negative (10) and having sensitivity to cold (78), UV radiation (5, 6), ionizing radiation, cisplatin, hydrogen peroxide (5), pH 8 (21), caffeine, sodium chloride, manganese chloride, calcium chloride (7), and HSP90 inhibitors (57, 97), and showing synthetic lethality with hsp82⌬ (68), as well as defects in sporulation (9, 14) and fluid-phase endocytosis (7). In this study, we also identified thr1⌬ and thr4⌬ mutants as being sensitive to high temperatures and, in the accompanying study, as starvation-cidal (49). We investigated the cause of these non-threonine auxotrophic phenotypes of thr1 and thr4 mutants by comparing phenotypes of various single-and double-threonine pathway mutants and determined that these phenotypes are the...

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Section: Discussionmentioning

confidence: 91%

Homoserine Toxicity in Saccharomyces cerevisiae and Candida albicans Homoserine Kinase ( thr1 Δ) Mutants

Kingsbury

McCusker

2010

Eukaryot Cell

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“…Neither of these properties by themselves explain why proline causes tagging because the azetidine analog (Aze), which does not cause tagging, also lacks an amide proton and has a constrained angle similar to proline (37,38). Is tagging related to the fact that the peptide bond of Xaa-Pro dipeptides can isomerize from the trans to the cis conformation at faster rates than dipeptides lacking proline?…”

Section: Discussionmentioning

confidence: 99%

“…These observations argue against isomerization being an important determinant of full-length tagging, but do not rule out this model, because cis-trans isomerization could be very different in solution than on the ribosome. Energy calculations show that XaaAze and Xaa-Pro have roughly similar conformational preferences but the smaller four-member ring of azetidine is predicted to lead to slightly more flexibility (37,38). This additional flexibility may permit the Xaa-Aze nascent chains to avoid steric clashes with release factors or help position the ester bond for hydrolysis.…”

Section: Discussionmentioning

confidence: 99%

Proline Residues at the C Terminus of Nascent Chains Induce SsrA Tagging during Translation Termination

Hayes¹,

Bose

Sauer

2002

Journal of Biological Chemistry

145

177

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The SsrA or tmRNA quality control system relieves ribosome stalling and directs the addition of a degradation tag to the C terminus of the nascent chain. In some instances, SsrA tagging of otherwise full-length proteins occurs when the ribosome pauses at stop codons during normal translation termination. Here, the identities of the C-terminal residues of the nascent chain are shown to play an important role in full-length protein tagging. Specifically, a subset of C-terminal Xaa-Pro sequences caused SsrA tagging of the full-length YbeL protein from Escherichia coli. This tagging increased when a less efficient stop codon was used, increased in cells lacking protein release factor-3, and decreased when protein release factor-1 was overexpressed. Incorporation of the analog azetidine-2-carboxylic acid in place of proline suppressed tagging, whereas incorporation of 3,4-dehydroproline increased SsrA tagging of full-length YbeL. These results suggest that the detailed chemical or conformational properties of the C-terminal residues of the nascent polypeptide can affect the rate of translation termination, thereby influencing ribosome pausing and SsrA tagging at stop codons.

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“…Given that incorporation of AZC into protein is known to cause reduced thermal stability or misfolding (12)(13)(14), the effects of the analog on gene expression are most likely due to its misfolding proteins. Two lines of evidence support this notion.…”

Section: Canavanine Treatment Does Not Mimic Azc Treatment-mentioning

confidence: 99%

“…Because the analog has one less carbon atom in its ring than does proline, the conformation of the polypeptide backbone is altered when AZC is incorporated in place of proline. Thus, incorporation of AZC into proteins causes reduced thermal stability or misfolding (12)(13)(14). Indeed, AZC-containing proteins bind avidly to Hsp70 chaperones in vivo (7).…”

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confidence: 99%

Misfolded Proteins Are Competent to Mediate a Subset of the Responses to Heat Shock in Saccharomyces cerevisiae

Trotter

Kao²,

Berenfeld

et al. 2002

Journal of Biological Chemistry

153

133

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Cells may sense heat shock via the accumulation of thermally misfolded proteins. To explore this possibility, we determined the effect of protein misfolding on gene expression in the absence of temperature changes. The imino acid analog azetidine-2-carboxylic acid (AZC) is incorporated into protein competitively with proline and causes reduced thermal stability or misfolding. We found that adding AZC to yeast at sublethal concentrations sufficient to arrest proliferation selectively induced expression of heat shock factor-regulated genes to a maximum of 27-fold and that these inductions were dependent on heat shock factor. AZC treatment also selectively repressed expression of the ribosomal protein genes, another heat shock factor-dependent process, to a maximum of 20-fold. AZC treatment thus strongly and selectively activates heat shock factor. AZC treatment causes this activation by misfolding proteins. Induction of HSP42 by AZC treatment required protein synthesis; treatment with ethanol, which can also misfold proteins, activated heat shock factor, but treatment with canavanine, an arginine analog less potent than AZC at misfolding proteins, did not. However, misfolded proteins did not strongly induce the stress response element regulon. We conclude that misfolded proteins are competent to specifically trigger activation of heat shock factor in response to heat shock.Eukaryotic cells respond to heat shock by the induction of a conserved set of proteins, the heat shock proteins, via transcriptional activation of the corresponding genes (1). In the budding yeast Saccharomyces cerevisiae, two distinct promoter elements mediate transcriptional activation in response to heat shock (reviewed in Ref.2). Heat shock elements (HSEs) 1 are found upstream of many heat-induced genes, e.g. HSP42 and SSA4. Heat shock factor binds to HSEs and is required for the induction of HSE-driven genes in response to heat shock. Stress response elements (STREs) are also found upstream of many heat shock-induced genes, e.g. CTT1 and DDR1, and bind the transcription factors Msn2 and Msn4 (2). Loss of both transcription factors compromises heat shock-induced expression of STRE-containing genes. Some heat shock-induced genes contain both HSEs and STREs in their promoters, e.g. HSP12, HSP30, and HSP104. The HSE and STRE regulons constitute the majority (if not all) of the genes that are specifically induced by heat shock (3).Rapid upshifts in temperature within the permissive growth range of yeast (so-called "temperature upshifts"), e.g. 23-36°C, result in the transient and selective induction of the heat shock genes (both HSE-and STRE-containing) and in the transient and selective repression of the 137 ribosomal protein genes (Ref. 4 and references therein). Heat shocks to nonpermissive temperature (e.g. to 42°C) also cause a global repression of gene expression not seen upon temperature upshift (4). Repression of the ribosomal protein genes by heat shock is dependent on activation of heat shock factor. Because these genes do not contain ...

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The effect of the L‐azetidine‐2‐carboxylic acid residue on protein conformation. I. Conformations of the residue and of dipeptides

Cited by 49 publications

References 28 publications

Homoserine Toxicity in Saccharomyces cerevisiae and Candida albicans Homoserine Kinase ( thr1 Δ) Mutants

Homoserine Toxicity in Saccharomyces cerevisiae and Candida albicans Homoserine Kinase ( thr1 Δ) Mutants

Proline Residues at the C Terminus of Nascent Chains Induce SsrA Tagging during Translation Termination

Misfolded Proteins Are Competent to Mediate a Subset of the Responses to Heat Shock in Saccharomyces cerevisiae

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