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N-terminal acetylation inhibits protein targeting to the endoplasmic reticulum.

Forte GM, Pool MR, Stirling CJ - PLoS Biol. (2011)

Bottom Line: Amino-terminal acetylation is probably the most common protein modification in eukaryotes with as many as 50%-80% of proteins reportedly altered in this way.Mutations in secretory signal sequences that led to their acetylation resulted in mis-sorting to the cytosol in a manner that was dependent upon the N-terminal processing machinery.Hence N-terminal acetylation represents an early determining step in the cellular sorting of nascent polypeptides that appears to be conserved across a wide range of species.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.

ABSTRACT
Amino-terminal acetylation is probably the most common protein modification in eukaryotes with as many as 50%-80% of proteins reportedly altered in this way. Here we report a systematic analysis of the predicted N-terminal processing of cytosolic proteins versus those destined to be sorted to the secretory pathway. While cytosolic proteins were profoundly biased in favour of processing, we found an equal and opposite bias against such modification for secretory proteins. Mutations in secretory signal sequences that led to their acetylation resulted in mis-sorting to the cytosol in a manner that was dependent upon the N-terminal processing machinery. Hence N-terminal acetylation represents an early determining step in the cellular sorting of nascent polypeptides that appears to be conserved across a wide range of species.

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Amino acid frequency at P2 of signal sequences versus cytosolicproteins.(A) Relative frequency of amino acids at P2 of a filtered set of 277 signalsequence-containing proteins from S. cerevisiae wascompared to a similar size group(n = 252) of randomly selectedcytosolic proteins. Frequency distribution between the groups differedsignificantly (p<0.0001,χ2 = 207.3 18 df). (B)Ratio of relative frequency of P2 residues between signal sequence(fss) and cytosolic(fcyt) proteins. Tryptophan was absentfrom the cytosolic group; therefore, nolog(fss/fcyt)value is plotted. P2 specificities of MetAP, NatA, and NatB are indicated.(C) Predicted methionine cleavage of signal sequence and cytosolic N-terminibased on relative P2 frequency. For complete datasets, see TablesS1–S4.
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pbio-1001073-g001: Amino acid frequency at P2 of signal sequences versus cytosolicproteins.(A) Relative frequency of amino acids at P2 of a filtered set of 277 signalsequence-containing proteins from S. cerevisiae wascompared to a similar size group(n = 252) of randomly selectedcytosolic proteins. Frequency distribution between the groups differedsignificantly (p<0.0001,χ2 = 207.3 18 df). (B)Ratio of relative frequency of P2 residues between signal sequence(fss) and cytosolic(fcyt) proteins. Tryptophan was absentfrom the cytosolic group; therefore, nolog(fss/fcyt)value is plotted. P2 specificities of MetAP, NatA, and NatB are indicated.(C) Predicted methionine cleavage of signal sequence and cytosolic N-terminibased on relative P2 frequency. For complete datasets, see TablesS1–S4.

Mentions: Signal sequence recognition and N-terminal processing both occur co-translationallyas the nascent chain emerges from the ribosome [10],[37]. We therefore decided toinvestigate whether secretory proteins might be subject to N-terminal processing ina similar manner to their cytosolic counterparts. As the P2 residue is the majordeterminant of N-terminal processing, we first surveyed the amino acid frequency atthis position for signal sequence-containing proteins versus cytosolic proteins(Figure 1A). Surprisingly,we found a significantly different frequency distribution between the two sets(p<0.0001, according to the χ2 test with 18degrees of freedom). Lysine, leucine, and arginine were most frequent at P2 insignal sequences but were rarely found at this position in the cytosolic set.Conversely, while serine and alanine were most frequent at P2 in cytosolic proteins,these were less evident in signal sequences. A clear pattern emerged when the ratioof frequencies were compared between the two classes of proteins (Figure 1B); small and acidicresidues were strongly biased towards cytosolic proteins, whereas large and basicones were favoured in signal sequences. The frequency of small residues at P2 incytosolic proteins predicts that ∼72% of these proteins would besubstrates for MetAP cleavage (Figure1C), in good agreement with empirical data from proteomic studies [2]. In contrastonly 23% of signal sequences would be predicted to be MetAP substrates (Figure 1C). Hence our data revealthat for signal sequences there appears to be a strong selection for P2 residuesthat would maintain the original N-terminal methionine.


N-terminal acetylation inhibits protein targeting to the endoplasmic reticulum.

Forte GM, Pool MR, Stirling CJ - PLoS Biol. (2011)

Amino acid frequency at P2 of signal sequences versus cytosolicproteins.(A) Relative frequency of amino acids at P2 of a filtered set of 277 signalsequence-containing proteins from S. cerevisiae wascompared to a similar size group(n = 252) of randomly selectedcytosolic proteins. Frequency distribution between the groups differedsignificantly (p<0.0001,χ2 = 207.3 18 df). (B)Ratio of relative frequency of P2 residues between signal sequence(fss) and cytosolic(fcyt) proteins. Tryptophan was absentfrom the cytosolic group; therefore, nolog(fss/fcyt)value is plotted. P2 specificities of MetAP, NatA, and NatB are indicated.(C) Predicted methionine cleavage of signal sequence and cytosolic N-terminibased on relative P2 frequency. For complete datasets, see TablesS1–S4.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3104963&req=5

pbio-1001073-g001: Amino acid frequency at P2 of signal sequences versus cytosolicproteins.(A) Relative frequency of amino acids at P2 of a filtered set of 277 signalsequence-containing proteins from S. cerevisiae wascompared to a similar size group(n = 252) of randomly selectedcytosolic proteins. Frequency distribution between the groups differedsignificantly (p<0.0001,χ2 = 207.3 18 df). (B)Ratio of relative frequency of P2 residues between signal sequence(fss) and cytosolic(fcyt) proteins. Tryptophan was absentfrom the cytosolic group; therefore, nolog(fss/fcyt)value is plotted. P2 specificities of MetAP, NatA, and NatB are indicated.(C) Predicted methionine cleavage of signal sequence and cytosolic N-terminibased on relative P2 frequency. For complete datasets, see TablesS1–S4.
Mentions: Signal sequence recognition and N-terminal processing both occur co-translationallyas the nascent chain emerges from the ribosome [10],[37]. We therefore decided toinvestigate whether secretory proteins might be subject to N-terminal processing ina similar manner to their cytosolic counterparts. As the P2 residue is the majordeterminant of N-terminal processing, we first surveyed the amino acid frequency atthis position for signal sequence-containing proteins versus cytosolic proteins(Figure 1A). Surprisingly,we found a significantly different frequency distribution between the two sets(p<0.0001, according to the χ2 test with 18degrees of freedom). Lysine, leucine, and arginine were most frequent at P2 insignal sequences but were rarely found at this position in the cytosolic set.Conversely, while serine and alanine were most frequent at P2 in cytosolic proteins,these were less evident in signal sequences. A clear pattern emerged when the ratioof frequencies were compared between the two classes of proteins (Figure 1B); small and acidicresidues were strongly biased towards cytosolic proteins, whereas large and basicones were favoured in signal sequences. The frequency of small residues at P2 incytosolic proteins predicts that ∼72% of these proteins would besubstrates for MetAP cleavage (Figure1C), in good agreement with empirical data from proteomic studies [2]. In contrastonly 23% of signal sequences would be predicted to be MetAP substrates (Figure 1C). Hence our data revealthat for signal sequences there appears to be a strong selection for P2 residuesthat would maintain the original N-terminal methionine.

Bottom Line: Amino-terminal acetylation is probably the most common protein modification in eukaryotes with as many as 50%-80% of proteins reportedly altered in this way.Mutations in secretory signal sequences that led to their acetylation resulted in mis-sorting to the cytosol in a manner that was dependent upon the N-terminal processing machinery.Hence N-terminal acetylation represents an early determining step in the cellular sorting of nascent polypeptides that appears to be conserved across a wide range of species.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.

ABSTRACT
Amino-terminal acetylation is probably the most common protein modification in eukaryotes with as many as 50%-80% of proteins reportedly altered in this way. Here we report a systematic analysis of the predicted N-terminal processing of cytosolic proteins versus those destined to be sorted to the secretory pathway. While cytosolic proteins were profoundly biased in favour of processing, we found an equal and opposite bias against such modification for secretory proteins. Mutations in secretory signal sequences that led to their acetylation resulted in mis-sorting to the cytosol in a manner that was dependent upon the N-terminal processing machinery. Hence N-terminal acetylation represents an early determining step in the cellular sorting of nascent polypeptides that appears to be conserved across a wide range of species.

Show MeSH